IL39142A - Probe photometer - Google Patents

Description

PROBE PHOTOMETER This invention is concerned with photometer apparatus and in particular with a photometer using a probe which may be inserted directly into a liquid or gas, to measure the light transmission through the fluid, and which may be used for example, for spectrophotometric, turbidity, colorimetric, densitometer, or other measurements.

This Invention relates to a probe for a photometer which comprises an elongated rigid member having an open recess defining a pair of spaced-apart transparent surfaces, a radiation sensing device mounted in said rigid member and positioned adjacent one of said surfaces and a solid transmission element positioned to carry radiation from a source to radiate between said surfaces to actuate said radiation sensing device In a manner responsive to radiation absorbing characteristics of a fluid located between said surfaces„ The photometer finds particular utility In spectrophotometric measurements in which a selected wavelength of light is directed through a fluid sample towards a photocell; the resultant output from the photocell being a measurement of the "optical transmission" of the sample at that wave-lengtho However, as indicated above, and as will become more evident as the description proceeds, the photometer has general utility for a wide variety of measurements involving the measurement of light transmission through a fluid sample.

The probe-type of photometer of the invention permits the aforesaid spectrophotometric measurements to be made by Immersing the photometer probe down into the fluid sample, the sample being contained, for example, in a test tube or other appropriate receptacle.

The probe-type photometer of the invention may conveniently be Included in an automatic system, whereby a series of test tubes may be transported to the robe hoto- meter station on a conveyor, and each test tube raised£under the probe to enable the probe to be immersed in the fluid sample contained therein. n this way, measurements may be made of the fluid samples contained in the successive test tubes, The outputs from the photometer for each subsequent measurement may then be recorded as a series of "optical density" or "percent concentration" readings.

As indicated above, the probe photometer of the invention also finds utility for determining turbidity in the fluid sample, for colorimetric measurements, for densitometer purposes, and the like.

There will now be described a probe-photometer using the probe as a component part in reference to the accompanying d awings, wherein; Figure 1 is a schematic representation of the apparatus and system, in which the probe photometer is a component; Figure 2 is a perspective representation of a probe photometer constructed in accordance with one embodiment of the invention; Figure 3 is a fragmentary perspective view showing a plug mounted at one end of the probe photometer of Figure 2; Figure is a circuit diagram appropriate for inclusion into the system of Figure 1 ; and Figure Is a circuit diagram of a fluid level sensing system.

The apparatus of Figure 1 includes a light source which is contained, for example, in a housing 10. The light source may be an incandescent lamp or any other appropriate source depending upon the use to which the apparatus of Figure 1 is to be placed. The light from the source emanates through outlets 12 and 1½ in the housing 10, any appropriate and known type of optical system being used within the housing to accom The housing 10 also includes a drive motor for a light chopper wheel 16. The light chopper wheel may be any known type, and it is rotatably driven so as to interrupt the light emanating from the outlets 12 and 1 ¼ at a rate determined by the number of clear and opaque segments on the wheel 16 and by the speed at which the wheel is rotated.

A probe photometer member 18 which will be discussed in more detail in conjunction with Figures 2 and 3 » is supported adjacent the housing 10, as shown in Figure 1 . The member 18 includes an elongated probe-like member which is configured to provide a pair of spaced-apart surfaces 1 and 20. As best shown in Figure 2, the probe-like member 18 may be formed of a glass tube. The glass tube has been found to withstand a wide variety of fluids in which it may be immersed. Howeverr, it is apparent that other substances may be used.

In the construction of the probe of Figure 2, the glass tube is softened at an intermediate point, for example, by the application of heat; and this intermediate point is deformed, as shown in Figure 2, so as to define the spaced-apart surfaces 19 and 20. However, the original passage through the tube is maintained in an unblocked condition around the deformed section. A photocell 22 of any appropriate type is mounted within the tube adjacent the surface 20. A light pipe 2* is also mounted in the tube, and it extends longitudinally down the tube so that its lower end is positioned adjacent the surface 19· As best shown in Figure 3, a usual electric plug 30 may be mounted at the upper end of the probe 2* , the plug having aplurality of prongs 32, as shown. The light pipe 18 may extend up through a central aperture in the plug 30, as shown in Figure 3 « The lower end of the glass tube may be closed by by heating the glass and drawing the end to a point.

The wires from the photocell 22 extend up the hollow passage in the glass tube and these wires may be connected to appropriate pins 32 of the plug 30* A thermistor element 36, or other temperature sensitive device, is mounted in the tube adjacent the photocell 22, and wires from this latter element may also extend up the passage in the glass tube to the other pins 32 of the plug 30. Likewise, a thermistor 38, or other temperature sensitive device, is mounted in the glass tube, adjacent the surface 19» but displaced up from the surface. Wires from this latter thermistor also extend up the passage and may be connected to the other pins 32 of the plug 30. The thermistor 38 responds to the corresponding change in temperature when the probe is dipped into a liquid, and when the fluid covers the level of the thermistor 38 so that it serves as a liquid level indicator.

The aforesaid liquid, for example, may be contained in a test tube o, as shown in Figure 1. In an automatic system, a series of test tubes, such as the test tube *f0, are transported on a conveyor rack successively to a position under the probe 18. Then, as each test tube arrives directly under the probe, automatic means raise the test tube up, so that the probe is immersed in the fluid contained in the test tube. The upward motion of the test tube continues until the liquid sensing thermistor 38 indicates that the probe is immersed in the liquid in the test tube, at which time the upward motion can be terminated and the corresponding reading taken. The temperature sensing device 36, on the other hand, senses the ambient temperature at the location of the photocell 22, and serves to compensate for the effect ambient temperature changes have on the photocell. being positioned between the outlet 12 and the upper end of the light pipe 24·. The wheel 4-2 may have different filters disposed at different angular positions about its center, and it may be turned by hand to interpose the various filters between the outlet 12 and the light pipe 24· for different spec-trophotometric measurements. One of the filter areas in the wheel 4-2 may be left void, so as to permit a second wheel mounted ciaxially with the ¾&eel 4-2 and over the wheel 4-2, to interpose a second series of light filters in the optical path of the light pipe 24·. In this manner, any desired number of optical filter wheels 4-2 may be stacked between the outlet 12 and the top of the light pipe, so that a large number of different light filters may be used.

A second photocell is positioned adjacent the outlet 14·. The photocells 22 and are connected to respective amplifiers 4*6 and 4-8 which, in turn, are connected to a synchronous detector 50.

In the operation of the apparatus and system of Figure 1, the light chopper wheel 16 is rotated at a predetermined rate. This means that the photocells 4-4- and 22 generate electric signals at a predetermined frequency. The amplitude of the output from the photocell remAins constant, whereas, the amplitude of the output from the photocell 22 is dependent upon the fluid in the test tube 40. The synchronous detector 50 provides an output which is representative of the output from the photocell 22, and which is independent of the ambient light level. This is because the system responds onlfc to signals whose frequency is established by the light chopper 16, and is unresponsive to other signals.

The liquid level sensing thermistor 38 is used to provide a control signal, which is used ina suitable control system (Figure 5) to cause the test tube kO to be lifted when be immersed Just below the level of the liquid in the test tube. This assures that all measurements will be made at a predetermined reference level with respect to the surface of the liquid as test tubes are successively moved under the probe and lifted into position to immerse the probe. The . temperature sensing device 36, on the other hand, produces a control signal which is used, as will be described, to assure that the output from the photocell 22 will be independent of changes in ambient temperature which result from different temperatures of the liquids in the various test tubes in which the probe is immersed.

As mentioned above, the probe 18 is preferably-composed of glass, since most plastic materials will dissolve in various fluids, and a glass probe tends to a more universal utility. However, obviously plastic or othe types of probes may be used if so desired.

Appropriate circuitry for the amplifiers k6 and ½8, and for the synchronous detector 50 of Figure 1 , is shown, for example, in Figure k. As shown in Figure k9 the probe temperature compensation thermistor 36 and the probe photocell 22 are connected across terminals 100,102, and 10* of the amplifier 6. The amplifier k6 includes an integrated circuit operational amplifier 106 of the type designated 809CE.

The terminal 100 is connected to one of the input terminals of the amplifier, and the output terminal is connected through a potentiometer 108 and resitor 110 to the second input terminal of the amplifier. The second input terminal is also connected to a resistor 112 which, in turn, is connected to a grounded capacitor 103. The potentiometer 108 may have a resistance, for example, of 500 kilo-ohms, the resistor 112 may have a resistance of 100 ohms, and the capacitor 103 may have a capacity of 500 microfarads.

The terminal 10t is grounded. The terminal 102 is connected to a grounded 1 kilo-ohm resistor 116 and to a potentiometer 118. The potentiometer 118 has a resistance, for example, of 750 ohms, and it is connected through a ¼70 ohm resistor 120 to the first input terminal of the integrated circuit amplifier 106 and to a ^.7 kilo-ohm grounded resistor 122. The potentiometer 118 permits a manual adjustment to he made as to the extent of temperature compensation provided for the photocell 22 by the thermistor 36.

The integrated circuit amplifier is connected to a positive 15 volt source and to a negative 15 volt source, as shown. The positive 1 volt source and the negative 15 volt source are connected to respective 1 microfard grounded capacitors 12* and 126. The integrated circuit amplifier 106 also has a terminal connected to a grounded capacitor 128, tte latter capacitor having a capacity, for example, of M-7 micro-microfarads.

The amplifier *+6 is, as will he appreciated, an integrated circuit operational amplifier. Its output is coupled through a 1 microfarad capacitor 130 and a microam-meter 133 to an output terminal 132. The other output terminal ^ )+ is grounded. A filter comprising a series resistor 136 and a shunt capacitor 138 is interposed between ¾ e capacitor 130 and the microammeter and output terminal 132.

The resistor 136 may, for example, have a resistance of 8.06 kilo-ohms, and the capacitor 138 may have a capacity of 300 microfarads. The microammeter may have a sensitivity of 50 microamperes for full scale deflection.

The output terminals 132 and 13½ are connected to has a resistance of 500 ohms, and the resistor 1 0 may have a resistance of 1 .91 kilo-ohms.

The reference photocell is connected to the amplifier kb which may comprise, for example, an NPN transistor 1 50 of the type presently designated 2N3053. The reference diode is connected, for example, to a grounded input terminal 1 2 of the amplifier S and to a second input terminal 1 5½. The input terminal 1 5*+ is coupled through a 10 microfarad coupling capacitor 1 56 to the base of the transistor 1 50.

The base is also connected to the common junction of a 100 kilo-ohm resistor 1 8 and h? kilo-ohm grounded resistor 160. The resistor 1 8 is connected to the positive 1 5 volt source. A 6,8 kilo-ohm resistor 162 connects the collector of the transistor 1 0 to the positive 1 volt source. A -,7 kilo-ohm resistor 16½ shunted by a 300 microfarad capacitor 166 connect the emitter of the transistor 1 50 to the ground.

The amplifier output from the transistor 1 0 is passed through a 10 microfarad coupling capacitor 168 to the base of an NPN transistor 170. The latter transistor, likewise, may be of the type designated 2N 3053· A diode 1 2 is connected between the base and collector of the transistor 1 0 these elements being grounded, as shown. The emitter of the transistor 170 is connected to the junction of the capacitor 130 and resistor 136.

The transistor 1 0 and its associates circuitry functions as a synchronous detector for the outputs from the operational amplifier 106. That is, the amplifier k8 introduces a constant amplitude signal to the circuit of the transistor 170, the signal having a frequency determined by the light chopper 16. The circuitry operates in known manner, so that the only output appearing on the microammeter 133 and across the out ut terminals 132 and 131* is the am lifier as the signal derived from the amplifier k8. The signal from the amplifier 106 of the synchronous frequency is that due to the light source in the housing 10, as interrupted by the light chopper 16, and has an amplitude which is a measure of the characteristic of the fluid in the test tube hO. In this way, the signal appearing on the microammeter 133 and across the output terminals 132 and 13½ is independent of ambient light changes. Also, due to the action of the thermistor 36, the output is also independent of any changed temperature might have on the probe photocell 22.

The probe Immersion sensing thermistor 38 of Figure 1 may be connected to the terminals 200 and 202 of the circuit shown in Figure 5· The terminal 202 is grounded, whereas the terminal 200 is connected to the base of a PNP transistor 20*4- and to the collector of a PNP transistor 206. Both these transistors may be of the type designated 2N2628. The emitter of the transistor 206 is connected through a 270 ohm resistor 208 to the positive 15 volt source. The base of the transistor 206, on the other hand, is connected to that source through a Zener diode 210 , and also is connected to a grounded 1 .8 kilo-ohm resistor 212.

The emitter of the transistor 20* is connected to the emitter of a similar PNP transistor 216, and the common emitters are connected to the positive 1 5 volt source through a 1 .2 kilo-ohm resistor 218. The collector of the transistor 216 is connected to a ½.7 kilo-ohm grounded resistor 220 and through a 1 kilo-ohm resistor 222 to the base of an NPN power transistor 22h. The latter transistor may be of the type designated 2N3053.

The base of the transistor 216 is connected to the movable contact of a 5 kiloohm potentiometer 226. The potenti is connected to the positive 1 5 volt source, as shown. i The emitter of the transistor 22k is grounded, and its collector is connected through a relay energizing coil 250 and through a k?0 ohm resistor 252 to a positive volt source. The circuit is such that when the thermistor 38 indicates a particular temperature change, the relay coil 2 0 causes the associated relay to be energized. The associated relay, for example, may control the aforesaid elevating mechanism, so that the mechanism will position each test tube HO of Figure 1 at a point where the thermistor 38 falls below the level of the liquid in the test tube. The potentiometer 226 may be adjusted, so that a positive control of the relay 250 is effectuated, by the change in temperature sensed by the thermistor 33 when it becomes immersed in the liquid in the test tube HO.

The invention provides, therefore, improved probe photometer apparatus which is capable of making appropriate measurements of fluid samples^ and which is independent of ambient light or temperature changes. The invention also Includes an Improved probe as a component of such apparatus, the probe nelng made in a commercially feasible manner, and being capable of easily being unplugged and plugged, when replacement is necessary.

It will be appreciated, or course, that while particular embodiments of the invention have been illustrated and described, modifications may be made. It is intended to cover such modifications in the claims. - -

Claims (3)

1. A probe for a photometer which comprises an elongated rigid member having an open recess defining a pair of spaced-apart transparent surfaces, a radiation sensing device mounted in said rigid member and positioned adjacent one of siad surfaces and a solid transmission element positioned to carry radiation from a source to radiate between said surfaces to actuate said radiation sensing device in a manner responsive to radiation absorbing characteristics of a fluid located between said surfaces.

2. The probe according to claim 2, in which said open recess is located near one end of said elongated rigid member .

3. The probe according to claim 1, in which said transmission element is an elongated light pipe. AGENTS FOR APPLICANTS