MXPA00000713A - Multiple resistive sensors for a coriolis effect mass flowmeter - Google Patents

Abstract

A circuit for utilizing multiple resistive sensors (109, 110) and in particular resistive temperature sensors while minimizing the number of conductors (308, 309, 310) necessary to measure the multiple sensors. The multiple sensors are connected in series and the voltage is measured at each node in the series connection of sensors. A switching device (F0) then opens to remove one of the sensors from the voltage supply (5v) allowing a measurement to be made of the resistance of the conductor between the temperature sensors and a remote transmitter (20). The measured sensor resistances are then compensated with the measured conductor resistance to obtain a conductor-length compensated resistance for each of the multiple resistive sensors.

Description

MULTIPLE RESISTIVE SENSORS FOR A CORIOLIS EFFECT MASS FLUJOMETER FIELD OF THE INVENTION This invention relates to an apparatus for using more than one resistive sensor in a Coriolis mass flowmeter. More particularly, the invention relates to a circuit for using more than one temperature sensor in a Coriolis mass flowmeter, while minimizing the number of necessary conductors between the flowmeter element and the transmitter flowmeter.

DECLARATION OF THE PROBLEM It is known to use a Coriolis mass flow meter for the measurement of mass flow and other information of materials flowing through a pipe as described in US Patent No. 4,491,025 published by J.E. Smith, et al, of January 1, 1985 and Re, 31,450 by J.E. Smith, February 11, 1982. These flow meters have one or more tubes for flow of right or curved configuration. Each tube configuration for REF .: 32412 flow in a Coriolis mass flowmeter has a set of natural vibration modes, which can be of a curved, torsional, radial or coupled type. Each tube for flow is excited or driven to oscillate to resonance in one or more of these natural modes. These natural modes of vibration of the vibration filling system are defined in part by the combined mass of the tubes for flow and the material within the tubes for flow. The material flows in the flow meter from a connected pipe on the admission side of the flowmeter. Then, the material is directed through the tube for flow or tubes for flow and leaves the flow meter to a pipe connected on the output side thereof.

An exciter or impeller applies force to oscillate the tube for flow. When there is no flow through the flowmeter, all points along a tube for flow oscillate with identical phase. As the material begins to flow, the Coriolis accelerations cause each point along the tube to flow to have a different phase with respect to the other points along the tube for flow. The phase on the intake side of the flow tube delays the exciter or impeller, while the phase on the exit side moves the exciter or impeller. The transducer sensors (pick-off) are placed in the tube for flow to produce sinusoidal signals representative of the movement of the tube for flow. The transducer sensors can be position, velocity or acceleration sensors. The phase difference between the two transducer sensor signals is proportional to the mass flow rate of the material flowing through the tube for flow or tubes for flow.

The fluid flows through a tube for flow that creates only a slight phase difference in the order of several degrees between the inlet and outlet ends of a tube for oscillation flow. When expressed in terms. of a measure of time difference, the phase difference induced by the fluid flow is in the order of tenths of microseconds less than the nanoseconds. Typically, a commercial flow meter must have an error of less than 0.1%. Therefore, a Coriolis type flowmeter should be designed only to measure exactly these slight phase differences.

The vibration characteristics of the vibratory structure of a Coriolis type flow meter change with changes in temperature. The vibration flow tube (s) are typically formed of a metallic material having a Young's modulus that changes with temperature. To maintain high accuracy in the measurement, the temperature of the vibratory structure is typically measured and compensation is made for the change in Young's modulus with changes in temperature.

A Coriolis type flowmeter system is comprised of two components; of a flowmeter element and a transmitter. The flowmeter element is the current sensor, which contains the vibration tube (s), through which the fluid flows, while the transmitter is the signal processing device that receives and processes the signals from the flowmeter element. The electrical connections between the flowmeter element and the transmitter are made through a multi-conductor cable. The protected or shielded cable is comprised of a protected or shielded conductor pair, which serves to provide an excitation signal to the exciter or driver, of a second and third protected or shielded conductor pairs for the transmission of signals from the transducer sensors and a triple protected or shielded conductor for the transmission of a signal from a temperature sensor located in the vibration flow tube. Typically a three-wire temperature sensor is used, since this allows a compensation of the resistance in the cable between the flow meter element and the transistor flow meter. This 9-wire cable is not a standard cable in the process control industry. Thus, whenever a Coriolis type flowmeter is installed using a remotely mounted transmitter of the flowmeter element, a non-standard, special cable (9-wire Coriolis type flowmeter cable) must be run between the flow meter element and the transmitter. This represents an additional expense for the user of the Coriolis type flowmeter.

As the Coriolis type flowmeter technology is developed, the demand in the operation and the changes in the geometry of the vibration flow tubes have originated the need to measure the temperature in the multiple points in the flow meter element. A measure of the temperature of the vibratory structure, for example, the flow tube (s), and a measure of the temperature of the non-vibratory structure may be necessary. Alternatively, a measurement of the temperature of a wet portion of the vibratory structure, and a measurement of the temperature of a non-wetted portion of the vibratory structure may be necessary. In any case, when more than one temperature sensor is used in existing Coriolis flowmeter designs, additional conductors are also required to those available on the 9-wire cable used in typical Coriolis type flowmeters. A cable that has more than 9 traditional conductors is a problem for several reasons. One reason is that even 9-wire cable is expensive. The fact of using a cable with even more conductors adds an additional expense for users of Coriolis type flowmeters. Therefore, whatever the number of sensors used in a given flowmeter, it is advantageous to minimize the number of conductors. For manufacturers of Coriolis type flowmeters, the additional conductors on the cable also mean additional connectors on both sides, on the flowmeter element and on the transmitter. This adds additional cost to the product and can also present problems if there is not enough physical space for the additional connectors. This is particularly true for intrinsic security applications. Compatibility is another reason why it is problematic to add additional conductors to the cable. Manufacturers of Coriolis mass flow meters can incur additional costs and complexities if different types of flow meter models require different cables. In addition, there is a large base of flow meters installed using 9-wire cables within which new designs of flow meters can be easily applied to replace old flow meters if the same cable can be used.

There is a need for a Coriolis mass flowmeter design that is provided for multiple temperature sensors, as long as the number of conductors between the flowmeter element and the transmitter is minimized. There is an additional need for a Coriolis type flow meter that uses two temperature sensors using the existing 9-wire cable, typically used with Coriolis mass flow meters.

PROPOSED SOLUTION The above and other problems are solved by the method and apparatus of the present invention comprising multiple temperature sensors in series. Each temperature sensor provides a separate temperature reading and a measurement of the resistance of the cable is also made to allow a compensation in the resistance of the cable. Periodically one of the temperature sensors of the series is disconnected with the other temperature sensors, and a measurement of the resistance of the cable is made. When the present invention is used with two temperature sensors, the same 9-wire cable used in existing single temperature sensor designs is used to measure two temperatures. When the present invention is used with more than two temperature sensors, then a minimum number of conductors is required compared to the existing Coriolis type flowmeter designs.

The designs of existing Coriolis mass flow meters require a conductor for each terminal and a resistive temperature sensor and at least one additional conductor in such a way that the resistance of the cable can be measured and compensated. In accordance with the present invention, the multiple temperature sensors are connected in series, and only the node points of the serial connection require conductors. No additional conductors are used to measure the resistance of the cable. One of the temperature sensors is periodically disconnected from the series connection in such a way that no current flows to such a temperature sensor. A measurement of the voltage across a conductor by itself is then possible, thereby providing a measure of the resistance of the cable.

The multiple temperature sensors are arranged in series. The number of conductors required (for temperature measurement) between the flow meter element (where the temperature sensors are located) and the transmitter is equal to 1 plus the number of temperature sensors. An interruption or switching device, which is located in the transmitter, is operable to disconnect one end of the serial connection of the temperature sensors of the transmitter's power supply. This ensures that no current flows through the temperature sensor at the disconnected end of the series connection. In this way, the voltage measured at the transmitter through the disconnected temperature sensor as compared to the voltage measured at the transmitter through a reference resistor, provides a measure of the resistance in the conductor between the transmitter and the sensor of temperature disconnected. This resistance of the cable is then subtracted or removed from the resistance measurements received from the temperature sensors. The resistance of the conductors between the transmitter and the flowmeter element changes with the temperature. In an environment where the temperature does not change rapidly, the measurement of cable resistance can be performed infrequently, for example, every 10 minutes. In an environment where the temperature changes rapidly, the strength of the cable can be measured more frequently, for example every 30 seconds. Although only the resistance of a single conductor is measured, all conductors are of the same length and the same gauge and are tied or packaged in the same cable. Thus, the resistance of a conductor is similar if not identical to that of the other conductors of the cable.

The present invention provides multiple temperature measurements with compensation of the length of the cable using a minimum number of conductors. In the case of two temperature sensors, only three conductors are necessary to make two separate temperature measurements and compensate for the length of the cable. In this way the existing cable of 9 wires extensively used with Coriolis type mass flow meters, can be accommodated with two temperature measurements.

DESCRIPTION OF THE DRAWINGS Figure 1 is a cross section of a mass flow system, Coriolis type, of right pipe, which employs dual temperature sensors; Figure 2 is a schematic of an example of an implement for a single temperature sensor circuit, such as that used in known Coriolis mass flow systems; Figure 3 is a schematic of an example of an implement for a dual temperature sensor circuit, in accordance with the present invention; Figure 4 is a more detailed scheme for a dual temperature sensor, in accordance with the present invention; Figure 5 is a flow chart describing the processing steps, which are controlled by a microprocessor to determine the temperature of the multiple temperature sensors according to the present invention, Figure 6 is a schematic for a circuit temperature sensor according to the present invention, which employs three temperature sensors.

DETAILED DESCRIPTION Coriolis Flowmeter System in General - Figure 1 Figure 1 shows a Coriolis type 5 flow meter system, which comprises a Coriolis 10 meter element and a transmitter 20. The transmitter 20 is connected to the meter assembly 10 via the cable multiple conductors 100. The transmitter 20 provides density data, mass flow rate, volume flow rate, and temperature by the path 26 to a utilization means (not shown). Although a Coriolis type flowmeter structure is described, it should be obvious to those skilled in the art that the present invention can be practiced or used in conjunction with a vibratory tube densimeter without the additional measurement capability provided by a Coriolis mass flowmeter.

The measuring element 10 includes a pair of flanges 101 and 101 ', multiple or diversification tubes 102 and 102'. The fluid enters the metering element 10 through one of the flanges 101 or 101 'and passes through the flow tube 103 leaving the flow element 10 through the other flange 101 or 101'. The flow tube 103 is surrounded by the balance tube 104. The flow tube 103 is connected to the balance tube 104 and the balance tube 104 is connected to the ends 105 and 105 'of the case or case 106. The ends 105 and 105 'form the ends of the housing or box 106. Figure 1 illustrates a right pipe for flow 103. Those skilled in the art will appreciate that the present invention can be applied to a flow meter system having a pipe for flow any geometry. In addition, because it is within the scope thereof, the present invention can be applied to a flow element having multiple tubes for flow through which the fluid flows.

The exciter or driver 107 is connected to balance the tube 104 at the midpoint of the balance tube 104. The transducer sensors 108 and 108 'are connected to balance the tube 104 and the flow tube 103. In one embodiment of the present invention , each of the transducer sensors 108 and 108 ', comprises a coil attached to the balance tube 104 and a magnet connected to the tube for flow 103 and are formed to move within the magnetic field generated when a periodic signal is applied to the coil . Those skilled in the art will recognize that transducer sensors of any design can be used, for example, accelerated electrons or potentiometers, and that the speed sensors described are only examples.

The counterweight 115 is connected to the balance tube 104 opposite to the diameter of the impeller or exciter 107. The mass of the counterweight 115 is determined by the density of the process fluid expected to be measured by the system 5. The temperature sensor of the tube for flow 109 it is attached to the flow tube 103, and the temperature sensor of the balance tube 110 is attached to the balance tube 104.

The cable 100 is comprised of the lead 111 carrying the excitation or pulse signal from the transmitter 20 to the exciter or driver 107, of the leads 112-113 which carry the transduction signals from the left and right sensors to the transmitter 20 , respectively, and of the conductor 114 carrying the temperature sensor information to the transmitter 20. The conductors 111-113 are currently two conductors each and the conductor 114 is currently three separate conductors which means that the cable 100 is comprised of 9 drivers.

The operation of the transmitter 20 which produces information of mass flow rate, volume flow rate and density is well known to those skilled in the flow measurement art, and is not part of the present invention. The circuitry that includes the temperature sensor 109 of the flow tube, the temperature sensor of the balance tube 110, the conductor 114 and the associated circuitry within the transmitter 20 form the basis for the remaining description.

It is obvious to those skilled in the art that the Coriolis 5 type flowmeter system is very similar in structure to a vibratory tube densitometer. The vibratory tube densitometers also use a vibratory tube through which the flow flows or, in the case of a densitometer of the type of sample, within which the flow is retained. Vibration tube densitometers also employ an excitation or impulse system to excite or propel the tube for flow to vibrate. Vibration tube densitometers typically use a single feedback signal, that is, from a single transducer, since a measure of the density requires only the measurement of the frequency and a measure of the phase is not necessary. The descriptions of the present invention can also be applied here, to vibratory tube densitometers.

Single Temperature Sensor - Figure 2 Figure 2 is a schematic for a circuit for known temperature measurement. Figure 2 illustrates a circuit for the measurement of temperature in a flow meter element 10 using a single temperature sensor 109. With reference to Figure 1, Figure 2 is a diagram showing the wiring necessary to use only the temperature sensor 109 of tube for flow. The conductor 114, which is part of the cable 100, is comprised of three conductors 201-203. The conductor 114 has a shield grounded by the path 210. The three wires 211-213 of the temperature sensor 109 are connected to the three terminals 204-206 in the flow meter element 10. The conductors 201-203 are connected to the terminals 204- 206 at one end, and terminals 207-209 at transmitter 20 at their respective other ends. Each of the conductors 201-203 have a conductive resistance modeled as resistance Rc in each of the conductors 201-203. The conductors 201-203 are substantially equal in length and gauge, and in this way the respective resistors are represented as equal. Although the resistance Rc in each of the conductors 201-203 is equal, the resistance R is not fixed. The value of the resistance Rc is determined by the length of the cable 100 and the temperature of the cable 100. For a given installation, the length of the cable 100 is fixed although this is rare, if it happens, it is known in the present that the system of Flowmeter 5 is calibrated in the plant. However, the temperature varies in time in a given installation. Thus, the value of the resistance Rc changes and must be compensated for a measurement in the temperature with the temperature sensor 109.

A voltage is applied by voltage reference through the supply resistor Rsum. In this example, a reference voltage of 5 volts is shown although any reference voltage can be used. The resistance Rsum / - the reference resistance Rref and the compensated resistance .comp, are selected in such a way that a voltage (V3-V2) through a temperature sensor 109 operating normally, does not exceed the interrupted voltage of the diode Di . Similarly, for diode D2. The temperature sensor 109 represents a typical three-wire resistive temperature detector. The temperature experienced by the temperature sensor 109 is measured by determining the resistance of the temperature sensor 109, which compensates the resistance for the resistance Rc and inserts such a resistance value into a standard equation, as discussed below.

The following equation illustrates the measurements made in the existing Coriolis type flowmeter systems to measure the resistance of the temperature sensor 109: (V3-V2) - (V2-V?) ÍIREF (O) = RTD O (EQUATION 1) Vi- Vo Equation 1, represents the difference through the voltage between the temperature sensor 109 (V3-V2) and the voltage across the resistance Rc (V2-Vi). The typical Resistive Temperature Device is a "100 Ohm (O) resistor". A 100-ohm DTR is measured by comparing the resistance of the DTR (temperature sensor 109) with a reference resistance of 100O (Rre_) • Once the resistance of the DTR is known, the temperature can be calculated using a characteristic equation for the particular type of DTR. The DTR manufacturers provide the characteristic equation for each DTR. Equation 2 is an example of a characteristic DTR equation. The value determined by solving equation 1 is inserted into equation 2 to determine the temperature experienced by the temperature sensor 109.

((DTR-100) * 2.56): Temperature = [(DTR-100) * 2.56] +1.25 (EQUATION 2) (V3-V2) 100O = Root + Rc (conductor 308) (equation 3; Alive Each type of DTR has a unique characteristic equation such as equation 2. The previous example is for a type of Heraeus 1PT100FKG 430.4-18-T-3.

This is how known Coriolis type flowmeter systems measure the temperature of the tube for flow. Note that a conductor 203 is dedicated to the full-time task of providing a means to measure the resistance (Rc) of the cable.

Dual Temperature Sensors - Figure 3 Figure 3 illustrates a circuit in accordance with the present invention for measuring temperature at two locations in a Coriolis mass flowmeter. The circuit of Figure 3 is similar to the circuit of Figure 2 except that there are two temperature sensors 109-110 and a Field Effect Transistor (TEC) F0 to disconnect the temperature sensor 110 from the voltage reference of 5. volts. Note also that the voltage V3 is measured on the side of the TEC F0 connected to the temperature sensor 110. The temperature sensors 109-110 have the resistors Ri09 ~ R? I0f respectively, which change according to the temperature experienced by each sensor.

The control line 307 is connected to a microprocessor (not shown in Figure 3) and determines when the TEC F0 is opened and when the TEC F0 is closed. When the TEC F0 is closed, the current flows from the voltage reference of 5 volts, to the TEC Fo and the conductor 308 (which has the resistance Rc), through the temperature sensors 110 and 109, and returns to the transmitter 20 through conductor 310 (which has a resistance Rc). The current flow continues through Rref and through RCOmp to ground. The Rref is, for purposes of this example, a resistance of 100O. When TEC F0 is closed, the following calculations are made.

(V2-V?) 100O = R109 + Rc (conductor 310) (EQUATION 4) Lives Equation 3 is used to calculate the resistance of the temperature sensor 110 (Ro) plus the resistance of the conductor 308 (Rc). Equation 4 is used to calculate the resistance of the temperature sensor 109 and the conductor 310 (Rc). The results of equations 3 and 4 can not be inserted directly into equation 2 to determine the temperatures because each of the results of equations 3 and 4 includes an amount of resistance equal to the resistance of the cable Rc. Periodically a measurement of the conductive resistance Rc is made by opening the TEC F0, and performing the measurements and calculations as described below. By opening the TEC F0, the current flows through the diode Di, through the conductor 309 (having a resistance Rc) and a temperature sensor 109, and returns to ground through the conductor 310 (which has a resistance Rc) resistance Rref reference and compensated resistance RCOmp- When TEC F0 is opened, the following calculations are carried out: (V2-V3) _ * 100O = Rc (driver 309) (EQUATION 5) V V0 (V2-V3) 100O = R109 * Rc (conductor 309) + Rc (conductor 310) (EQUATION 6) V1-V0 Since there is no current flowing through the temperature sensor 110 when the TEC F0 is opened, the voltage (V2-V3) represents a voltage drop because only the current flowing through the conductor 309 has a resistance Re-When this voltage is divided by the voltage across the reference resistance Rref and the result is multiplied by the value of the reference resistance Rref of (100O), the value of the resistance Rc is obtained. As noted above, the conductors 308-310 are all substantially equal in length and gauge and all are subjected to the same temperature in this manner it is assumed that the measured resistance of one of the conductors is equal to the resistance of each conductor. the remaining drivers. In one embodiment of the present invention, the result of equation 5 is subtracted from the results of equations 3 and 4 to determine the resistance of temperature sensor 110 and temperature sensor 109, respectively. Then, these values are inserted one at a time as the "DTR" value in equation 2 to determine the temperature experienced by each of the temperature sensors.

In another embodiment of the present invention another calculation is made to provide a second estimate of Rc and the two values of Rc are averaged to determine an Rc value used as described above. The result of equation 4 is subtracted from the result of equation 6 that allows an estimate of the resistance of conductor 109 (Rc). Thus, in this Rc mode, it is measured as follows: (EQUATION 6 - EQUATION 4) + EQUATION 5 Rc (EQUATION 1) This method for determining the resistance Rc is more accurate than simply using the result of equation 5, because equation 7 uses an average of the two measures of the resistance of conductor 109. This average value of Rc is obtained from the equation 7 then subtracted or subtracted from equations 3 and 4 to obtain the resistance values for the temperature sensors 110 and 109, respectively.

Dual Temperature Sensors and the Transmitter 20 - Figures 4-5 The common elements between the figures are referred to with the same reference numbers. Figure 4 illustrates the circuit of Figure 3 in combination with the necessary support and control circuitry of the transmitter 20. The control line 307 that controls the operation of the TEC F0, is connected to the control output 412 of the microprocessor 409. microprocessor 409 is configured to periodically interrupt the open TEC F0 as described above. In one embodiment of the present invention, the TEC F0 is opened in an interrupted manner for approximately 0.8 seconds every ten minutes to effect the necessary measurement of the Rc. The TEC Fo is representative of an interruption device. Those skilled in the art will recognize that any suitable interruption device such as, but not limited to, a transistor can be used instead of TEC F0. The damping resistors 414-418 ensure that the circuitry of the transistor 20, itself does not affect the resistance measurements of the temperature sensors 109-110. In one embodiment, the resistors 414-418 have values of 10KO and the resistances Rsup ..- Rref and Rcomp have values of 1.74KO, 100O and 3.01KO, respectively. The reference resistance Rref is highly accurate, for example, towards 0.1% and 10 parts per million per degree C.

The four voltages V0-V3 are read at inputs I0-I3, respectively, of multiplexer 401. Multiplexer 401 bypasses or switches between inputs I0-I3 to produce one of voltages V0-V3 at a time at output 403. The voltage level at the output 403 is transmitted via line 404 to the voltage converter at frequency ("V / F") 406. The V / F 406 converts a voltage input at the input 405 to a corresponding frequency output. at the output 407. The frequency at the output 407 is transmitted via line 408 to the microprocessor 409 and read at the frequency input 410 of the microprocessor 409. The operation of the multiplexer 401 is controlled by a signal on the path 420 from the control output 411 of the microprocessor 409 to provide each of the voltages V0-V3 in succession at the output 403. The microprocessor 409 receives the frequency representing each voltage measurement at the input 410 and stores a value for each frequency in memory of 419. Then, the Central Processing Unit ("CPU") 421 uses the values stored in memory 419 to compute all equations 3-7 to produce a path through output 413 for the temperature experienced by temperature sensor 109 and the temperature experienced by temperature sensor 110 The microprocessor 409 is a commercially available microprocessor such as the MC68HC705C9A-CFN manufactured by Motorola. The operation of such microprocessors to perform the aforementioned calculations and tasks is well known to those skilled in the art.

Figure 5 is a flow diagram illustrating the steps of the process executed by the microprocessor 409 to produce the values for the temperature sensors 109-110. The processing starts at element 500 and proceeds to step 501. During step 501 a voltage reference is applied to the series connection of the multiple temperature sensors. With reference to Figure 4, the voltage reference of 5 volts is canceled, if not yet ready, and the TEC Fo is closed during step 501. Then the processing proceeds to step 502.

During step 502, the voltage is measured at each node of the serial connection of temperature sensors. For example, an appropriate control signal is sent to the control output 402 of the multiplexer 401 to successively interrupt or bypass the voltages V0-V3 to the V / F 406. As described above with respect to Figure 4, the microprocessor counts the frequency corresponding to each of the Vo ~ V voltages and stores an appropriate value in the memory 419. The processing then proceeds to step 503.

During step 503, the resistance is determined through each temperature sensor. Of course, with the measurements made to where, the resistance through each temperature sensor also includes the resistance of the conductor by which the necessary voltages are measured. The calculations made during step 503 correspond to equations 3 and 4, described previously. Processing follows in step 504.

During step 504, a switch is opened to remove one end of the series connection of the temperature sensors from the voltage reference. With reference to the circuit of Figure 4, the F0 is opened in response to a control signal by the path 307 from the control output 412 of the microprocessor 409. Then the processing proceeds in step 505.

During step 505, the voltage is measured at each node of the series connection of the temperature sensors. For example, an appropriate control signal 402 is sent to the multiplexer 401 to successively interrupt the voltages Vo ~ V3 to V / F 406. As described above with respect to FIG. 4, the. microprocessor 409 counts the frequency corresponding to each of the voltages V0-V3 and stores an appropriate value in memory 419. The processing then proceeds to step 506.

During step 506 the resistance across one of the conductors is measured to allow a subsequent compensation for the conductive resistance. In the example of Figure 4, the resistance of the conductor is determined using either only the calculation of equation 5, or the calculations of formulas 5-7 to determine an average amount for Rc. The processing then continues in step 507.

During step 507 the value of Rc calculated during step 506 is subtracted from the resistance of the temperature sensor calculated during step 503. This step generates a compensated resistance value for each temperature sensor connected in series. Then the step continues in step 508.

During step 508 each of the compensated sensor resistance values are converted to one of temperature using, for example, a characteristic equation such as equation 2. The shape of equation 2 depends on the current temperature sensor model, and is supplied by the manufacturer of the temperature sensor. Then the processing concludes in step 509. n Temperature Sensors - Figure 6 Figure 6 describes a circuit using a third temperature sensor RN which is connected to the transmitter 20 by a conductor 601 having a resistance Rc. R may be, for example, a temperature sensor mounted in the housing or housing 106 in FIG. 1. With the closed FET F0, the voltages Vo ~ V3 and VCn are measured. Then the following calculations are made to determine the resistance through the conductors and the temperature sensors: (V3-V2) _ * 100O = R110 + Rc (conductor 308) (EQUATION 8) (V2-V 100O = R109 (EQUATION 9) (V? -VN) 100O = RN + Rc (conductor 601) (EQUATION 10) Note that in the case of equation 10, the resistance of the temperature sensor 109 is measured directly without any conductive resistance component. However, to determine the resistances of the temperature sensor 110 and the RN temperature sensor, further processing is needed. The TEC F0 opens with a control signal on the path 307. The voltages Vo ~ V3 and VN are measured, and the following calculations are made to determine the resistance of the Rc conductor:c.

(V2-V3) 100O = Rc (conductor 309) (EQUATION 11) VN-VQ Equation 11 allows a direct measurement of the resistance Rc of conductor 309. As described above, an average value of the conductor resistance can be obtained R with additional calculations as follows: (Vz-V. * 100O = Rc (conductor 309) + R109 (EQUATION 12) EQUATION 12 - EQUATION 9 + EQUATION 11 Rprom (EQUATION 13) Equation 12 includes. the resistance of the R109 temperature sensor. In this way an average Rprom value is obtained for the resistance of the conductor 309. As noted above, it is assumed that each of the conductors 308-309 and 601 have the same resistance since these are substantially of the same length and gauge and they experience substantially the same temperature. Then the Rprom is subtracted subtract from equation 8 and equation 10 to obtain the compensated values for R110 and RN, respectively. As you can see, R109 is measured directly.

Figure 6 and the associated calculations of Equations 8-13 illustrate that the present invention is applicable to any number of temperature sensors by arranging the N sensors in series and providing a switch that disconnects one of the sensors from the voltage supply to provide a measure of the resistance of the driver.

Although the present invention has been described in terms of resistive temperature sensors, those skilled in the art will recognize that any type of resistive sensor can be used in place of a temperature sensor. For example, one could use a strain gauge that indicates strain or deformation in the form of a variable resistor instead of one or more of the temperature sensors described here. The present invention can be applied using any sensor that indicates a condition that changes its resistance. The essence of the present invention applies equally to any configuration.

This is so that it is expressly understood that the claimed invention is not limited to the description of the preferred embodiment, but covers other modifications and alterations within the scope and spirit of the inventive concept.

It is noted that in relation to this date, the best method known to the applicant, to implement said invention is that which is clear from the manufacture of the objects to which it refers.

Having described the invention as above, property is claimed as contained in the following:

Claims (16)

1. A transmitter measuring a compensated condition of the conductive resistance for each of the n resistive sensors connected in series, characterized in that it comprises: n + l conductors for connecting said n resistive sensors in series with said transmitter; a first of said n + l conductors, connected to a first of said n resistive sensors at a first end of said n resistive sensors connected in series; n-l of said n + l conductors connected to said n resistive sensors, in series between each of said n resistive sensors; a second of said n + l conductors, connected to at least one of said n resistive sensors at a second end of said n resistive sensors connected in series, wherein said second conductor connects said n resistive sensors to ground through a resistor of reference; an interrupting means connecting a voltage supply in said transmitter to said first conductor; means for measuring the resistance of the conductor connected to said first conductor for measuring the resistance of the conductor, said first conductor responding to said means of interrupting said voltage supply; means for connecting said n-l conductors and said second conductor for measuring a resistance indicative of the condition through each said n resistive sensor, responsive to said voltage supply that is connected to said n resistive sensors in series; and a responding means for a measurement of said conductive resistance, and said measure of said resistance indicative of condition for determining a compensated resistance condition of the conductor, for each of said n resistive sensors and said conductive resistance or conductor.

2. The transmitter of claim 1, characterized in that said means for measuring the resistance of a conductor includes: a timing means for periodically opening said interruption means, for disconnecting said voltage supply means from the first end of said series of sensors; means for measuring a conductive voltage between said first end of said n resistive sensors, and one of said n + l conductors connected between said n resistive sensors responsive to said voltage supply that is disconnected from said n resistive sensors in series; an average to measure a reference voltage through said reference resistance; and means for comparing said conductive voltage with said reference voltage for determining said conductive or conductor resistance.

3. The transmitter of claim 2, characterized in that said means for comparing includes: means for dividing said conductive voltage by said reference voltage to provide a voltage ratio; and means for multiplying said voltage ratio by a reference value where said reference value is the value in ohms of said reference resistance.

4. The transmitter of claim 3, characterized in that said reference value is 100 ohms.

5. The transmitter of claim 1, characterized in that said n resistive sensors in series include: one of said nl conductors, same having a first end connected to said n resistive sensors in series, between two of said n resistive sensors, and in the second end of said transmitter.

6. The transmitter of claim 5, characterized in that said measurement means indicative of the condition includes: means for measuring a first sensor voltage between said first end of n resistive sensors in series, and said second end of said one of said nl conductors; means for measuring a reference voltage through said reference resistance; and a means for comparing said first sensor voltage with said reference voltage, for determining said first sensor resistance wherein said first sensor resistance including the resistance of a first of said n resistive sensors and the resistance of said first conductor.

7. The transmitter of claim 6, characterized in that said means for comparison includes: means for dividing said first sensor voltage by said reference voltage to produce a first sensor voltage ratio; and means for multiplying said first voltage sensor ratio by a reference value wherein said reference value is the value in ohms of said reference resistance.

8. The transmitter of claim 7, characterized in that the reference value is 100 ohms.

9. The transmitting circuit of claim 6, characterized in that said measuring means indicative of the condition includes: an edip for measuring a second sensor voltage, between said second end of one of said n-1-conductors and said second conductor; means for measuring a reference voltage through said reference resistance; and a means for comparing said second sensor voltage with said reference voltage, for determining said second sensor resistance wherein said second resistance sensor includes the resistance of one second of said n resistive sensors, and the resistance of said second conductor.

10. The transmitter of claim 9, characterized in that said comparison means includes: means for dividing said second sensor voltage by said reference voltage to produce a second voltage sensor ratio; and means for multiplying said second voltage ratio by a reference value, wherein said reference value is the value in ohms of said reference resistance.

11. The transmitter of claim 10, characterized in that said reference value is 100 ohms.

12. The transmitter of claim 7, characterized in that said determining means includes: a first subtraction or subtraction means for subtracting said resistance from the conductor of said first resistance sensor, to determine a first compensated sensor resistance; a second subtraction or subtraction means for subtracting said conductive resistance or the conductor of said second resistance sensor, to determine a second compensated sensor resistance; means for converting said first compensated sensor resistance and said second sensor compensated resistance, to a first condition and a second condition, respectively.

13. The transmitter of claim 2, characterized in that said comparison means includes: means for measuring a first voltage between said second end of said one of nl conductors, and a second end of said second conducting conductor to said n resistive sensors in series themselves which are disconnected from the voltage supply by said means of interruption; means for measuring a first reference voltage, through said reference resistor responsive to said n series reference sensors, which are disconnected from said voltage supply by means of the switch; means for comparing said first voltage with said first reference voltage to determine a first sensor resistance wherein said first sensor resistance includes the resistance of one of said n resistive sensors in series, the resistance of one of said nl conductors, and the resistance of said second conductor; means for measuring a second voltage between said second end of said one of the n-l conductors, and a second end of said second conductor responding to said n resistive sensors, which are connected to said voltage supply by said interruption means; means for measuring a second reference voltage across the reference resistor, when said series sensor is connected to said voltage supply; means for comparing said second voltage with said second reference voltage for determining a second sensor resistance, wherein the second sensor resistance includes the resistance of said one of the n resistive sensors in series and the resistance of said second conductor; a means responsive to said first sensor resistance, said second sensor resistance, and said conductive or conductor resistance to calculate an average conductor resistance.

14. The transmitter of claim 13, characterized in that said means for calculating includes: means for subtracting or subtracting said second sensor resistor from said first sensor resistor, to generate a conductor or estimated conductor resistance; means for adding said resistance of the conductor or conductive to said resistance of the estimated conductor or conductor, and dividing them in two to obtain said resistance of the average conductor.

15. The transmitter of claim 1, characterized in that one of said resistive sensors in series, is a resistive temperature sensor and said condition is the temperature.

16. A method for measuring a conductive resistance or compensated conductor, condition for each of said n resistive sensors connected in series, characterized in that it comprises the steps of: applying a voltage of 5 volts to each of the n resistive sensors connected in series; measure a voltage in each node of said n resistive sensors connected in series; determining, a response for said measurement voltage at each of said nodes, a voltage across each of said n resistive sensors; compare said voltage to. through each of said n resistive sensors with a reference voltage across a reference resistor to obtain a sensor resistance for each of said multiple resistive sensors; disconnecting a conductor connected to a first of said n resistive sensors of said applied voltage; and measuring a voltage of the conductor through said conductor; comparing said conductor voltage with a second reference voltage through said reference resistance to obtain a conductive resistance of said conductor; subtracting or subtracting said second conductor or conductive resistance from each of said sensor resistors obtained by said n resistive sensors to obtain a resistance compensated for each of said multiple resistive sensors; and converting each of said compensated resistors to a condition reading, wherein each of said condition readings is associated with one of said n resistive sensors.