FR2671651A1 - SYSTEM FOR MEASURING TWO VARIABLE QUANTITIES. - Google Patents

Abstract

A first and a second variable quantity, for example a pressure and a temperature, the value of the first variable quantity being affected by the changes in the value of the second variable quantity, are measured by a system comprising a sensor (20) having a resistive bridge element (21). A first and a second signal, resulting from the imbalance and the change in overall resistance of the bridge element under the action of the respective first and second variable quantities, are sent to an electronic module (22). An application specific integrated circuit (ASIC 46) carried by a printed circuit board (PCB 23), processes the first and second signals "with calibrated values stored in an EEPROM memory (45) carried by a card (PCB 24) ) of the module (22) and provides signals representative of the corrected true value of the first variable quantity and the value of the second variable quantity. An advantage of the system is that power is supplied to the system and the data measures are supplied by the system on a single pair of conductors, which is not possible if two sensors are used, i.e. one for each variable quantity.

Description

i

  SYSTEM FOR MEASURING TWO VARIABLE QUANTITIES

  The present invention relates to a system for

  the measurement of two variable quantities.

  We often need to measure two variable quantities, for example pressure and temperature, when the output of a sensor measuring one of the variable quantities, for example pressure, is affected by changes in the other variable quantity, for example temperature An example of such a necessity is the case of measuring and displaying the internal pressure

  vehicle wheel tires, for example tire-

  aircraft landing gear wheels, all

  by monitoring and at the same time indicating the temperature

  Overheating of the wheels In particular in an application to an aircraft landing gear, there is also a need for a system for measuring the pressure and the temperature to be produced in the form of a

  light unit and minimal dimension.

  A similar requirement may be encountered, for example, in the measurement of load or torque and

temperature.

  GB -A-2 122 757 describes a device for measuring one or more parameters, for example the pressure and /

  or the temperature, existing inside a pneumati-

  that on a vehicle wheel A disadvantage of this dis-

  positive is that when you want to measure both the pressure

  temperature and temperature, a pressure sensor and a temperature sensor must be provided

  each a pair of electric power supply conductors

stick for their food.

  US-A-4 703 650 describes a circuit for coding the value of two variables measured in a vehicle wheel tire, which makes it possible to transmit the value of the variables to the vehicle body However, a system

  which this coding circuit is a part of uses two

  to measure the two variables, for example a

  silicon temperature sensor to measure the temperature

  ture and a piezoresistive gauge to measure the pressure.

  An object of the present invention is to provide a system for measuring two variable quantities with

a single sensor.

  Consequently, according to a first aspect, the present invention provides a method for measuring a first and a second variable quantity, comprising the operations of: activation of detection means comprising a resistive bridge element; obtaining a first signal representative of the first variable quantity, supplied by the detection means due to the imbalance of the resistive bridge element under the action of the first variable quantity, this first signal also depending on the effect of the second variable quantity on the overall resistance of the resistive bridge element; measuring the overall resistance of the resistive bridge element, to obtain a signal representative of the second variable quantity; processing of the first and second signals with

  the outputs of the detection means obtained during the

  tailgating in a range of the first and second variable quantities, in order to obtain a true corrected value

  for the first variable quantity; and.

  emission of signals representative of the

  their true corrected for the first variable quantity and

  of the value of the second variable quantity.

  In another aspect, the present invention provides a system for measuring a first and a

  second variable quantities, comprising means of

  tection including a resistive bridge element, means

  activation of detection means, means of

  retention of a first signal supplied by the detection means

  tection due to the imbalance of the resistance bridge element

  tif under the action of the first variable quantity, means for measuring the overall resistance of the resistive bridge element to obtain a second signal which is

  representative of the second variable quantity, of the mo-

  yen of memory to contain the values supplied by the detection means when they are calibrated in a range of the first and second variable quantities, of the means for processing the values of the first and second

  signals with the calibrated values contained in the mo-

  yersde memory to obtain a true corrected value

  of the first variable quantity, and of the means of emission

  signal representative of the true corrected value of the first variable quantity and the value

of the second variable quantity.

  Examples of the first variable quantity

  to be measured are pressure, load and torque, tan-

  say that the second variable quantity is usually

temperature.

  The detection means can comprise a piezoresistive cell, other possibilities being for example a resistive bridge element on a membrane in

stainless steel or ceramic.

  The overall resistance of the bridge element

  sistive can be determined by measuring the current which

  circulates in a high precision resistance

  connected in series in a supply line of the bridge, so that the second signal is obtained in the form

of a voltage signal.

  The memory means to store the values

  their provided by the detection means during their

  calibration in a range of first and second quan-

  variable entities may include a consultation table

  tation contained in an electronic programmable read-only memory

traceability erasable (EEPROM).

  The means of treatment of the first and second-

  me signals with calibrated values from mo-

  memory yen can include analog to digital conversion means to convert

  output voltage signals, supplied by the detection means

  due to the imbalance of the resistive bridge element,

  and the voltage signals representative of the resistance

  this total of the resistive bridge element, in a nu-

  meric and to provide binary data signals

  for addressing the EEPROM memory.

  The processing means can include

  in addition to logical means of interpolation for the treatment

  data extracted from the EEPROM memory and the

  calculation of a true corrected value for the first quan-

variable tity.

  The signal transmission means may include

  dre also means of converting the correct value

  true age of the first variable quantity and the value

  their of the second variable quantity in binary coded data Means can be provided for generating frequency change modulation (FSK) signals representative of the binary coded data and for modulating the FSK signals on a power signal to the detection means, in order to transmit these signals

at a remote location.

  The processing means may include an application-specific integrated circuit (ASIC) mounted

  on a printed circuit board (PCB).

  The PCB of the ASIC circuit can be part of an electronic module connected to the detection means and the electronic module can also comprise an EEPROM memory PCB and a supply PCB connected so as to receive a power signal and to supply

  a voltage reference signal to supply the mo-

  detection yen and PCBs from ASIC and EEPROM.

  Thus, the present invention provides a system

  teme for measuring two variable quantities, for example a pressure, a load or a torque, and a temperature, which requires a single detection cell having a first signal output which is proportional to the

  first variable quantity but which is also influen-

  created by the second variable quantity The value of the second variable quantity can be obtained by measuring a characteristic of the detection cell, -and a

  second signal which is proportional to the second quan-

  variable tity is processed with the first signal in an electronic module of minimum size and weight, to obtain a true corrected value of the first

  variable quantity The true corrected value of the first

  re variable quantity and the value of the second variable quantity are supplied and, if desired, transmitted

  to a remote data receiving station A forward

  particular stage of a system conforming to the present invention

  tion is that energy is supplied to the system and the

  data measurements of two different quantities vary

  bles are supplied by the system on a single pair of conductors, which is not possible if two are used

  sensors, i.e. one for each variable quantity.

  The invention will now be described in more detail, by way of example and with reference to the accompanying drawings in which:

  Figure 1 is a circuit diagram of a system

  teme according to an embodiment of the invention;

  Figure 2 is * a schematic side view il-

  polishing the mechanical construction of an electronic module

  as part of the system shown in Figure 1;

  Figure 3 is an exploded schematic view il-

  polishing the positions of three printed circuit boards

  constituting the electronic module shown in the figure

  gure 2; and Figure 4 is a schematic representation of an application-specific integrated circuit, provided

  on one of the printed circuit boards of the electro- module

fuck.

  Referring to FIG. 1, a measurement system

  of a first and a second variable quantity, for example the pressure and the temperature, comprises a unique detection device which is constituted, in

  the present embodiment, by a piezo cell

  resistive 20 The cell 20 is a one-piece device in the form of a silicon wafer on which is implanted a Wheatstone bridge circuit 23, for example of the type sold by KELLER AG, 119 St Gallerstrasse,

  Winterthur, Switzerland Cell 20 is connected to a mo-

  dule electronics 22 which includes three printed circuit boards (called PCBs in the following) 23, 24 and 25,

  bridge input lines 26 and 27 connected to pins

  ches 28 and 29, respectively, of the electronic module, and bridge output lines 31 and 32 connected to

  pins 33 and 34, respectively, of the electronic module.

  The PCV 25 is a power PCB which is connected by pins 35 and 36 to receive a power signal of 31.25 k Hz The power input to the PCB

  is protected by a bidirectional Zener diode 37.

  The power signal is applied to the input of a re-

  blocker and a voltage regulator via a capacitor 38 which has a low impedance

  to the power signal but a high impedance at the

  frequency modulation modulation channels which can

  can be modulated on the power signal for trans-

  data mission as described below The signal from

  power is rectified by two diodes 39.40 and a con-

  densifier 41 then converted into a direct voltage of volts by a voltage regulator 42 This voltage is used on lines 43 and 44 to supply the

cell 20 and PCBs 23 and 24.

  The PCB 24 carries an electrically erasable programmable read-only memory (EEPROM) 45 which contains, in the present embodiment, a 32 × 16 matrix look-up table which is used, as described below for storing correction data of the signals supplied by cell 20 which are representative of the

first variable quantity.

  PCB 23 carries an application specific integrated circuit (ASIC) 46 which is connected to pins

  33 and 34 by lines 47 and 48, respectively, in front of

  lesson in receiving the variable voltage signals supplied by the cell 20 due to the imbalance of the bridge 21

  under the action of the first variable quantity on the cell

  lule 20 The output of the bridge is non-linear and it varies

  also with variations in the second quantity will

  reliable, usually temperature, which affects

  overall resistance of the bridge 21 The overall resistance of the bridge 21 is checked by measuring the voltage across a high precision resistor 49 which is carried on the PCB 23 and connected in line 26 The voltage across the resistor 49 is applied to ASIC 46 on lines 50,51 and, using the characteristics

  known of the resistance, we calculate the current which

  pour the bridge and determine the overall resistance of the bridge. PCB 23 also carries resistors 52,

  53 and a capacitor 54 The resistor 52 is a resistor

  current limiting tance which uses the power signal to constitute a clock for the ASIC 46 The resistor 53 is used to modulate the FSK signals carrying the data supplied by the ASIC, on the signal

  of power In order not to lose the greatest part

  tie of the FSK signal, the value of resistor 53 is not large enough to protect the output to a

  remote data reception station (not shown

  on line 43 and pin 35, against high voltages of the power signal, and capacitor 54 is therefore necessary to act as a reducing filter

  the level of the power signal on pin 35.

  Figures 2 and 3 show the configuration

  mechanical tion of the electronic module 22 The PCBs 23,24 are circular in shape and are connected to each other by copper wires 55 soldered to each PCB The wires position the PCBs relative to each other

  to others and allow the transmission of signals

  be PCB As the ASIC 46 circuit is a component

  in surface mount ceramic, PCB 23 is manufactured

  made of ceramic to avoid problems resulting from differential expansion between ASIC 46 and PCB 23 PCB 24 and 25 carry common components

  with through hole pins and so they're fa-

  polyimide bricks The whole assembly is sealed with

  a suitable coating compound having a low den-

  sity and a low coefficient of thermal expansion The external surface of the ceramic PCB 23 does not have

  tracks but it is provided with studs for connection

  55 copper wires and is also provided

  pins 28,29,33,34 for connection to cell 20.

  This last connection is made by means of a circuit

  cooked in monolayer polyimide 56 (see Figure 2).

  As shown in Figure 4, the ASIC 46 has three stages, namely a conversion stage

  analog-digital 60, a separate communication stage

  rielle 61 and a logical interpolation stage 62 Le

  first stage 60 comprises a switch 63, an amplifier

  64 programmable gain sensor and an analog converter

  que-numerique 65 The first stage 60 receives two inputs,

  the first entrance being the exit of the bridge 21 which is pro-

  portable at the first variable quantity and at the two

  xth variable quantity, and the second input being the voltage measured across the resistor 49 which is

  proportional to the variation of the second quantity will

  reliable but relatively insensitive to the variation of the first variable quantity The input to the amplifier 64 is switched by the switch 63 between the input coming from the bridge 23 and the input coming from the resistor 54, at the clock frequency , and the gain of amplifier 64 is

  adjusted accordingly Each time a payment is made

  re readings, reverse the polarity of the amplifier

  64 and analog-to-digital converter 65 to

  to cancel any errors caused by

  offset sions The analog-to-digital converter

  provides two numeric words, one of which describes two

  tenth variable quantity and the other describes the first

  variable quantity to which cell 21 is subjected.

  These words are sent to a separate communication circuit.

  rielle 61 has serial communication stage 61 which

  transmits the most significant bits of the two words to the me-

  moire EEPROM 45 as addresses to allow extraction

  correction data stored Each word indicates

  correction data is stored in the EEPROM

  in the form of a byte and its inverse, to per-

  set to perform data integrity check

  born on the data extracted from the EEPROM The data extracted from the EEPROM consist of four bytes and their inverse These data are checked and are transmitted

  to the logic interpolation circuit 62 a of the logic stage

  that of interpolation 62, together with the bits of

  low weight of the two digital words coming from the

  analog-digital vertisseur 65 These are used

  read in combination with the data from the EEPROM to calculate the true value of the first variable quantity The corrected pressure data are

  modulated on the power signal of 31.25 k Hz at mo-

  yen of modulation techniques by frequency change

  ce and a digital frequency synthesizer 70 doing

  part of stage 62 of ASIC circuit 46.

  After assembly of the cell 20 and the electronic module 22, the assembly is calibrated within a range

  operating requirements of the first and second quan-

  variable tities For example, if the first and second variable quantities are pressure and temperature, two voltage output signals are obtained, one of which Vp is proportional to pressure but influenced by temperature, and the other of which Vt is proportional to the

  temperature but not significantly influenced by the pressure

  In order to avoid the storage of a large number of va-

  their, which would normally be necessary to obtain the required precision, we use an adjustment method

  curve to define the values to write in the ta-

  ble of matrix consultation in the EEPROM memory 45, using a laptop computer 67 (FIG. 4) which is

  connected by a serial data line 68 and a li-

  serial clock 69 at EEPROM 45.

  In operation, when energy is supplied-

  negates at pins 35.36, the power signal of 31.25 k Hz enters the supply PCB 25 and is rectified and regulated to provide a DC voltage of 5 volts for

  the power supply of the PCBs of ASIC and EEPROM 24 and 25, res-

pectively, and from cell 20.

  ASIC 46 reads four memory locations

  in EEPROM 45 to obtain the pressure gain values

  value and temperature for the input amplifier The gain values plus their inverse values are read

  to confirm the operation of the EEPROM memory (before the

  lonnage, we load systematic values into it 1 EEPROM) We then adjust the gain to obtain the full range of the analog-digital converter and

  the gain values are reloaded in the EEPROM.

  The ASIC 46 then reads the differential pressure and uniform end inlet temperature values.

  that for at least 100 samples The polarity of the

  trées is reversed during alternating clock cycles ,,

  in order to eliminate by shifting the average

  sensor and amplifier management The analog to digital converter supplies the establishment logic

  average which provides one byte of data for the temperature

  erasure and pressure, respectively These data are then truncated into a 9-bit address (5 bits

  for temperature and 4 bits for pressure).

  The 9-bit word is used for addressing eight locations in the EEPROM The eight locations

  are determined by incrementing the tempera-

  ture, of a bit, then of the pressure part to obtain a sequence of four points We repeat this treatment

  for the four inverse data locations We check

  relies on data and reverse data for alteration

  tion, and we obtain four correspondence points If an alteration is detected, an error word is passed to the FSK output and no further processing is carried out If the data is good, the ASIC then uses the weight bits low for pressure and temperature,

  so as to perform a linear interpolation for cal-

calculate a true pressure value.

  The corrected or true pressure value and the

  temperature values are coded in four binai words

  res for transmission to the remote receiving station

  data (not shown) which may include an or-

  The four binary words Wl, W 2, W 3 and W 4 have the same structure, which is as follows: 1 start bit (logic state 0) 8 data bits, with the most significant bit first 1 parity bit (data bits + parity = even) 1 stop bit (logic state 1) The words W 1, W 2 and W 3 are identical and have a value

* which represents the pressure.

  The word W 4 has a value which represents the time

  temperature. The ASIC includes built-in tests (BITE) which verify that the cell inputs are not short-circuited at 5 V, low impedance at OV and in open circuit. The BITE also checks the EEPROM memory and the ASIC circuit itself. even if an error is detected, this is indicated by an error code in the

  words W 1, W 2 and W 3 The ASIC also checks that the pres-

  sion is within a required range, for example

  from O to 1750 k Pa (O at 254 psi) in this embodiment

  The ASIC does not report an error for a press.

  sion greater than 1750 k Pa but any pressure greater

  is limited to an indication of 1750 k Pa.

  Examples of the data bits for the words W 1, W 2 and W 3 in the pressure range are as follows: Pressure k Pa Decimal Binary

0 O 0000 0000

6.9 6.9 0000 0001

13.8 13.8 0000 0010

1,744.2 1,744.2 1,111 1,101

  1751.1 and above 1751.1 1111 1110 An error code 1111 1111 is sent when the BITE of the ASIC circuit detects: (a) The failure of the EEPROM memory test (b) A failure of the pressure cell

  (c) Failure of the ASIC circuit self-test.

  The code 'not equipped' with the code W 4 is llll 1111.

  The power signal can be applied to pins 35,36 from the remote receiving station.

  tion of the data and in this case the data output from the ASIC can be transmitted to the data receiving station by means of FSK signals modulated on the power signal In this case, the data in the form of words is transmitted to the synthesizer of digital frequency 70 in the third stage 62 of the ASIC which generates one of two frequencies A frequency of 2225 Hz is generated for logic state 1 and a frequency of 2025 Hz is generated for logic state 0 These frequencies are modulated on the power signal of 31.25 K Hz and transmitted to the data reception station where the data is decoded and made continuously available.15 It is understood that, although a system conforming to this can be used invention for measuring a pressure and a temperature, for example the inflation pressure of a vehicle wheel tire and the temperature of heating of the wheel, it can also be used for measure other variable quantities, by

  example a load or a couple and a temperature.

Claims (14)

  1. Method of measuring a first and a   second variable quantity, characterized by the operations-   tions of: activation of detection means comprising a resistive bridge element, obtaining a first signal representative of the first variable quantity supplied by the   detection due to the imbalance of the bridge element   sistive under the action of the first variable quantity, this first signal also depending on the effect of the second variable quantity on the overall resistance of the resistive bridge element; measuring the overall resistance of the resistive bridge element to obtain a signal representative of the second variable quantity; processing of the first and second signals with   the outputs of the detection means obtained during the   tailgating in a range of the first and second quan-   variable tities, in order to obtain a true corrected value for the first variable quantity; and transmitting signals representative of the true corrected value of the first variable quantity and of the   value of the second variable quantity.   2. The method of claim 1, further characterized in that the measurement operation of   the overall resistance of the resistive bridge element   takes the measurement of the current flowing in a resistor   this high precision connected in series in a line bridge supply.   3. System for measuring a first and a second variable quantity, which comprises means   detection (20) comprising a resistive bridge element   tif (21), means (25) for supplying means for   tection, and means (23) for obtaining a first si-   general provided by the detection means due to the   equilibrium of the resistive bridge element under the action of the first variable quantity, characterized by means (49) for measuring the overall resistance of the   resistive bridge to obtain a second signal which is re-   presentation of the second variable quantity, memory means (45) for storing the values supplied by the detection means during their calibration in a range of the first and second variable quantities,   means (46) for processing the values of the first and two   x signals with the calibrated values contained in the memory means in order to obtain a true corrected value of the first variable quantity, and means (70)   transmitting signals representative of the correct value   true age of the first variable quantity and the value   their of the second variable quantity.   4. System according to claim 3,   characterized in that the means for measuring the resistance   this overall resistive bridge element include   means for measuring the current flowing in a resistor   high precision tance (49) connected in series in   a supply line to the bridge (26).   5. System according to claim 3 or claim 4, characterized in that the means of méée   memory include an electric programmable read-only memory   erasable (EEPROM, 45) containing a table   consultation of the values of the first and second quanti-   variable tees supplied by the detection means during   of their calibration within an operating range.   6. The system of claim 5, further characterized in that the processing means   first and second signals with standard values-   born from the memory means comprise analog to digital conversion means (65) for converting the voltage signals supplied by the detection means (20) due to the imbalance of the   resistive bridge (21) and the voltage signals represented   of the overall strength of the bridge element   tif in digital form and for providing binary data signals suitable for addressing the memory EEPROM (45).   7. The system as claimed in claim 6, further characterized in that the processing means further comprise logic interpolation means (62) for processing the data extracted from the EEPROM memory and for calculating a true corrected value of the first variable quantity.   8. The system of claim 7, further characterized in that the means for transmitting   signal include means of converting the   corrected for them by the first variable quantity and by the value of the second variable quantity in binary coded data. 9. System according to claim 8,   further characterized by means for generating   frequency modulated signals (FSK) represent   binary coded data, and means (70) for modulating the FSK signal on a power supply signal of the   detection means, for transmission to a place   so much. 10. System according to any one of   claims 3 to 9, characterized in that the means for   processing include an application-specific integrated circuit (ASIC, 46) mounted on a printed circuit board (PCB, 23). 11. The system of claim 10, further characterized in that the PCB (23) of the ASIC circuit forms part of an electronic module   (22) connected to the detection means (20).   12. The system of claim 11, further characterized in that the electronic module   (22) further includes an EEPROM memory PCB (24).   13. The system of claim 11 or claim 12, further characterized in that the   electronic module (22) further comprises a PCB of a-   the power supply (25) connected so as to receive a   power and to provide a reference signal   voltage to supply the detection means (20).   14. System according to any one of   previous claims, characterized in that the   detection means include a piezoresistive cell tive.