US3823575A

US3823575A - Cryogenic apparatus

Info

Publication number: US3823575A
Application number: US00150284A
Authority: US
Inventors: J Parel
Original assignee: University of Melbourne
Current assignee: University of Melbourne
Priority date: 1971-06-07
Filing date: 1971-06-07
Publication date: 1974-07-16
Anticipated expiration: 1991-07-16

Abstract

A cryogenic apparatus is disclosed for use in biological sciences having automated controls and using the Joule-Thomson effect. A supply of gas flows to a control unit which includes a solenoid gas valve. If the gas pressure and flow rate are within acceptable limits, the valve will permit flow from the control unit to a probe to effect cooling of the probe by the JouleThomson effect.

Description

United States Patent 1191 Parel [4 July 16, 1974 CRYOGENIC APPARATUS 3,548,829 12/1970 Reynolds 128/3031 1751 Invenwn Jean-Marie Pare, Miami, 3:253:33? 131133} 53131;;:1::1:::::::::;::::::::::: 13313833 [73] Assignee: The University of Melbourne,

Parkville, Victoria, Australia Primary Examiner-Meyer Perlin [22] Filed: June 7 1971 Attorney, Agent, or Firm-Dennison, Dennison, Townshend & Meserole [21] Appl. No.: 150,284

[57] ABSTRACT k s A cryogenic apparatus is disclosed for use in biologi- [58] Fie'ld 128/303 1 cal sciences having automated controls and using the c Joule-Thomson effect. A supply of gas flows to a con- [5 6] R f Ct d trol unit which includes a solenoid gas valve. If the gas e erences l e pressure and flow rate are within acceptable limits, the UNITED STATES PATENTS valve will permit flow from the control unit to a probe 3,393,679 7/1968 Crump 128/3031 to effect cooling of the probe by the Joule-Thomson 3,398,738 8/1968 Lamb l28/303.l ff t 3,439,680 4/1969 Thomas.. 128/3031 3,536,075 10/1970 Thomas 128/303.1 12 Claims, 9 Drawing Figures D.C.-0R A.C. r7 SUPPLY LINEI 14 l 9 7 1 REGULATOR POWER ELECTRON; l

SUPPLY GAS COUPLING I '51 34 19/ GAS FLOW I L SQLENQD I PRESSURE DETECTOR VALVE l 55 20 I ELECTRDNlC I CONTROL I l2 15 FOOT SWITCH PATENIEDJULI 61am lma REGULATO l1 J C 7 l 00 NM l 1.. O U W0 W. C S M u u OE L m y D. C ou "A u \L IIPS R N T 0 R It 7 TT E E L. 0 W D L C I: 2 L E E F R W L S AS cw. P MJ PAIENIE JUL 1 e 1914 SNEETZUF U 69 N i E 73 ELECTROMAGNETlC 1 LATCH\NG SYSTEM g 72 K I LOW SPEED TIME BASE 70 ONE SHOT MULTWIBRATOR SELF LOCKNG 757 SOLENOU VALVE 105 E omvmc WW I f f i 74 I I a, g

v 0,4 84- L L FL\P I A I I FLOP E loo 5 f P BR l r 82 95 BL ONE SHOT MULTl- 99 VIBRATOR E3 PART I I PROGRAMMABLE VOLTAGE /77 REGULATOR powza' SUPPLY LEVEL DETECTOR H ri08 LEVEL ozracroa LEVEL DETECTOR l K K 95 2m m 92.

LEVEL DETECTOR LEVEL DETECTOR :95 1 95) 79 ADJUST ?j"LEVEL DETECTOR I BRIDGE LEVEL DETECTOR 2)) 80 LEVEL DETECTOR FLOW z PRESSURE Z9 91 DETECTOR/ E 3 PART 17 i 92 PATENTEB saw u or 6 vs 667 m HEATER c a mma w 8 THERMO COUPLE g o. z

a? PROBE 5 l SENSOR g) 7 I 57 E \7 2 m I 2 g MICRO E 90 SWH'CH .U.LLU.LLU.LL H\GH SPEED MULTMBRATOR h 87/ AUDlO GENERATOR :8 157 112 89 swncu 7 LOW SPEED MULTMBRATOR m" lffi. 3 -PART ZZZ CRYOGENIC APPARATUS This invention relates to improved cryogenic apparatus and particularly to such an apparatus which has wide applications in the biological sciences and particularly to such an apparatus in which the controls are automated.

Cryogenic apparatus for use in surgical and similar applications as have previously been proposed are of one of a number of forms. Some of these apparatuses use liquid gases, some frozen solids and some vaporization of gases from the liquid to the gaseous state. Still others have been proposed using the Joule-Thomson effect, i.e. adiabatic expansion, to provide cooling and it is to this latter type of apparatus that the present invention relates. The Joule-Thomson cooling effect is provided when a gas under high pressure is passed through an orifice, or plug after which the gas expands into a relatively unrestricted area, thus doing internal work and provided the initial temperature is less than the inversion temperature, the gas cools and heat is drawn from this surrounding area.

The basic concept of using the Joule-Thomson effect in cryogenic apparatus is not new, although it is not common. The first known apparatus is one developed by Verzella in approximately 1965, which apparatus has certain disadvantages specifically in that it only cooled at the rate of approximately 1 C per second and thus normally took some time over 50 seconds to reach its operating temperature, minus 50 celsius. Also, it had no way whereby the temperature of the probe could rapidly be brought to ambient temperature. This apparatus was followed by an apparatus developed by Amoils, which practically was much more successful, could reach a lower temperature, and could reach this temperature at the rate of approximately C per second. The apparatus did have disadvantages in that control functions were minimal and incorrect or dangerous operation could occur.

Subsequently further development work was done by Ruiz, but again the Ruiz apparatus was not fully acceptable.

lt is a first object of the present invention to provide a cryogenic apparatus which cools by the use of the Joule-Thomson effect which is fully controllable and which at the same time gives a rapid cooling rate.

A further object of the invention is to provide such an apparatus which will either not operate, or cease operating on abnormal variation in gas pressure or gas flow.

A still further object is to provide an apparatus of this general type in which operation of the apparatus is prevented unless the tubes of the apparatus have been correctly flushed before assembly.

There is still a further object to provide an apparatus of this general type in which the probe to be used can be readily removed and replaced whereby the apparatus can be used for a wide range of applications.

Another object is to provide an apparatus of this general type which has an audible and/or visible warning system whereby an operator is notified of machine or gas failure.

Another object of the invention is to provide a means whereby pressure and flow rate changes in gases can be monitored.

The apparatus of the invention has basically been designed for ophthalmic surgery, but is has been designed so that it can be used as a cryogenic probe for a large variety of apparatus. Thus, for example, the apparatus with different types of probes can be used for various cryogenic operations on the human body, but can also be used to provide, for example, microscope specimens which are frozen or can be used in other biological applications where areas of more or less limited freezing is necessary.

In its broadest sense the apparatus includes an electronic thermodynamic control and a probe, the control being arranged for connection to a gas source whereby gas can be passed to the probe to effect cooling by the Joule-Thomson effect characterized in that gas cannot pass to the probe unless the gas pressure and flow rates are within predetermined limits.

Preferably the arrangement is such that on blockage of a gas line further operation is prevented.

The invention also provides an apparatus as described hereinbefore wherein the probe includes a heating element and wherein the device has a control whereby the heating element operates on the probe reaching a selected temperature to thereby control the heat gradient in the probe to prevent inadvertent adhesion of the probe away from its tip to the person or article with which the device is used and to prevent discomfort or damage to the users hand. The heating element preferably continues to operate after cooling ceases until a predetermined temperature is reached.

The invention also includes a probe as herein defined having a replaceable tip. The apparatus may also be providedwith an automatic flushing device which ensures the gas passages in the unit is clear.

The invention also includes a pressure and flow detector for gases including a first element in a relatively unrestricted volume, a second element in a restricted volume and means whereby the overall resistive changes of the elements can be identified and thus pressure changes identified and wherein the relative resistive changes in the element due to gas flow can be identified.

Normally the output of these elements can be fed to a bridge circuit for comparison purposes, the bridge having six arms and two outputs from one of whicha pressure analogue can be obtained and from the other a flow analogue can be isolated.

The apparatus can be used with any form of gas which will give satisfactory cooling by the Joule- Thomson effect and gases which have been foundto be practically acceptable are such gases as carbon dioxide, nitrous oxide, Freon l2 and Freon 22. It is to be understood that the gas concerned does not necessarily have to be a gas which is normally considered'a good refrigerant, although Freon is mentioned hereinbefore, although developed as a refrigerant, as it is not essential for the invention to liquefy the gas under relatively high pressures.

The control unit is preferably arranged to screw straight onto the top of the gas cylinder and is provided with a master gas control valve which is itself connected directly to the cylinder. In this way there are no leads between the cylinder and the control valve which have been found to be a source of trouble in previous devices, either because of the mechanical difficulty of locating the cylinder and the device at a distance when interconnected and also because variation in the relative positions of the cylinder and the device has tended to lead to damage of the gas lines therebetween and a possible leakage of gas when the device is being used.

In order that the invention may be more readily understood and put into practice reference will be made to the accompanying drawings in which:

FIG. 1 is a schematic view of the control unit of the invention;

FIG. 2 is a block diagram illustrating the general operation of the invention;

FIG. 3 (which is shown on three sheets) more specifically illustrating the control systems of the invention.

FIG. 4 is a drawing of the flow meter and pressure detector of the invention;

FIG. 5 is the circuit of the flow meter and pressure detector, its associated bridge and output;

FIG. 6 is a schematic view of one form of probe of the invention; and

FIG. 7 is an enlarged view of the probe tip.

In order to describe the invention we will first refer to FIG. 2 to give some idea of the features of the invention. We shall then describe the flow meter and pressure detector arrangement and its operating circuit. The arrangement of the probe will then be described together with the functions which occur on operation. Finally we shall discuss at some length the operation of the schematic diagram of FIG. 3.

The block diagram of FIG. 2 shows the control unit 10 within the dotted lines, the gas cylinder 11 to the left of the control unit, the probe 12 to the right of the control unit and a foot switch 13 also connected to the control unit. It is to be understood that it is preferred the control unit 10 is connected directly to the gas cylinder as illustrated in FIG. 1. This not only prevents the possibility of damage to the unit because of a trailing connection, but also minimises the possibility that a fault can occur between the gas cylinder and the control unit. It will also be understood that if flexible lines are being used under pressure damage can occur if these lines are kinked or if, by any chance, the pressure is greater than that for which the lines are designed.

The gas is directly connected to the regulator 14 which may be a manual or automatic regulator and which permits control of the output pressure. Preferably this regulator is associated with a pair of pressure gauges, gauge 150 which gives a continuous metering of the pressure within the cylinder and gauge 160 the pressure on the outlet side of the regulator.

The regulator is in connection with a flow meter 29 and a solenoid valve 29'. The flow meter 29 is arranged to provide monitoring of both the gaspressure and flow rate and to initiate a control function to prevent or stop operation of the device if either of these parameters extend above or below acceptable limits. The operation of the device is controlled by operation of the solenoid valve.

The solenoid valve 29 is basically adapted for direct control by the operator either by the use of a foot switch 13 or by the use of a micro switch 17 on the probe 12. The solenoid valve in association with a latching circuit control circuit carries out a further function in flushing the unit flow control circuit.

From the solenoid valve the gas passes to a coupling circuit 18 from whence it is directed to the micro probe 12.

The electronic part of the circuit is shown in the block diagram of FIG; 2 as power supply 19 and the electronic control 20. The operation of this will be further described hereinafter.

Referring now to FIG. 4 we show the specific form of flow meter and pressure detector 29. This has a body 30 which is connected to a gas line 31 from the regulator and as illustrated the connection is by a screwed collar 32. The outlet 33 of the device is connected to a further gas line 34 which passes to the solenoid valve of the unit and this connection is also made by a screwed collar 35.

It can be seen that the device has two chambers, the upstream chamber 36 and a downstream chamber 37, the upstream chamber being of substantially larger diameter than the downstream chamber. Mounted at the junction between the two chambers is an orifice plate 38 having a plurality of apertures 39 therein. Mounted coaxially in the two chambers are a pair of

windings

40 and 41, the winding 40 being designated the pressure transducer and the winding 41 the flow transducer, although as will be described hereafter these designations are not strictly correct. The two windings are connected by means of

conductors

42a, 42b and 420, not illustrated in FIG. 4 into a bridge circuit which is shown in FIG. 5. The

transducers

40 and 41 each comprise one arm of a bridge, the other two arms of the bridge being adjustable resistances R43 and R44. The complete bridge is in fact a six arm bridge, the other two arms R45 and R46 also being adjustable resistances. The two bridge outputs both include the junction between transducer 40 and resistance R43 and the pressure output P is also connected to the junction between resistances R45 and R46. The flow output F is connected to the junction between the flow transducer 41 and resistance 44.

The operation of the flow meter and pressure detector depends on the variation of the resistances of the

transducers

40 and 41 with temperature. This variation can either be an increase or decrease of resistance with increase of temperature, the effect being usuable to provide the parameters required.

Considering first the situation when the pressure in the

chambers

36 and 37 increase. As the chambers are interconnected there will be no effective pressure differential between the two chambers. With increased pressure there is greater molecular activity and thus the temperature of the transducers tends to decrease as the molecules being heated by contact with the transducers tend to transmit their energy to other molecules and finally to the walls of the device more rapidly than when the pressure is lower. Thus provided proper calibration a pressure reading can be obtained from the resistance of either winding. Transducer 40 is used to provide this effect, but it can be seen that either transducer would be equally satisfactory. By calibration of the bridge consisting of transducer 40, resistance R43, resistance R45 and resistance R46, we can obtain an analogue to the absolute or relative pressure and the output of this bridge is passed through an operational amplifier AMP 47, which may be provided with a feed back circuit 48.

The flow situation is somewhat different in that if flow can be passed close to a coil the molecules tend to be heated, thus lowering the temperature of the coil and as the molecules are flowing passed the coil, a dynamic, but not static equilibrium can be set up. By the arrangement of the orifice plate 38 and a baffle plate 49, the pressure transducer 40 is effectively protected from the cooling effect of flowing gas, whereas because of the arrangement of the compartment 37 the flowing gas acts strongly on the flow transducer 41. There develops a temperature differential between the two transducers, which differential is dependent on the rate of flow of gas.

Use is made of this resistance differential by the bridge consisting of the

transducers

40 and 41 and the resistances R43 and R44. The output of this bridge is transmitted to the operation amplifier AMP 50, the flow amplifier which may be provided with a feed back circuit 51. As flow increases, the temperature of transducer 41 decreases and thus the voltage differential between the two arms of the bridge vary. It can be seen that the effect of pressure changes is minimal in this case as on change in pressure the temperatures of both transducers change and can be arranged to change effectively identically.

In order to provide the various required functions we use an interconnection 55 between the control unit and the probe which consists of a pair of concentric tubes, which are adapted to transmit the gas and an eight point electrical connector positioned around the periphery of the tubes.

The tubes are preferably made of polytetrafluroethylene and in one practical form of the device the inner tube has an inner diameter of 0.79 mm. and has an outer diameter of approximately 1.6 mm. The outer tube has an inner diameter of 1.68 mm. and an outer diameter of 2.5 mm. The arrangement is such that on any distortion of the inner tube it contacts the outer tube thus increasing the effective strength of the tube. The electrical connections are positioned around the outer tube and in the preferred form of the device connections are provided for earth, for a thermocouple, for the defrosting heater, for the hand switch and for a probe sensing circuit. These electrical connections will be described further in the description of the circuit of FIG. 3.

The probe 56 may be of any desired material and is of such a size that it can be readily held in the hand. One form of probe is illustrated schematically in FIGS. 6 and 7. Preferably there is a reduced portion 57 adjacent the tip and this reduced portion is provided with a sleeve 58 of a material which has poor heat conducting characteristics and preferably a sleeve of polytetrafluroethylene.

The tip 59 itself extends from this reduced portion and the tip or the end and the tip can be replaceable.

The tip or tips at its end may be partly isolated by a fibreglass or other nonconducting material to minimize heat transfer from the tip to the probe.

The gas passes through a central bore 60 in the probe from whence it can pass to the tip.

In the illustrated form of the tip it has a central-needle 61 which has an opening 62 at its outer end adjacent one side. The outer casing of the tip has an extension 63 positioned beneath the opening and may preferably be provided with a recess 64 in this extension directly in line with the opening. Alternatively it may have a sphere or other required shaped end portion thereon. As the gas leaves the inner needle 61 under high velocity it strikes the extension or shaped portion, heat is absorbed therefrom thus the extension is cooled. It is to be understood that the particular arrangement of inner needle and tip may be varied depending on the purpose for which the probe is to be used and it will also be realised that depending on the purposes of the probe the whole configuration of the tip can be varied greatly. In order to make the probe of most universal application, it is of course desirable to ensure that the gas flow into the body of the probe can be sufficient to cool a relatively long and large tip.

Mounted adjacent the tip is a thermocouple, the position of which is indicated by 65 which thermocouple can be so calibrated as to give a relatively accurate reading of the temperature at the extension 63 or the shaped portion. Mounted in the body of the probe adjacent the tip is a heater element the location of which is indicated at 66, which serves both to ensure that the tip warms rapidly when low temperature is no longer desired and which at the same time acts to revent the operators hand being frozen to the probe in use.

In operation it is only necessary to connect the control unit 10 on to a gas cylinder 11 and to a normal electrical power source 67.

The units regulator 14 is normally adjusted for a particular type of gas and then left in this position as long as the same gas type is being used.

As soon as the cylinder 11 is connected a visible monitoring of the input and output gas pressures is obtained from gauges and and once the device is turned on there is complete monitoring of the gas parameters electronically. Provided the probe line is not connected several seconds after switching on the unit the gas line is flushed by automatically opening the solenoid valve 16 for a short time, preferably 0.1 of a second. If the gas pressure is at a critical minimum this function does not occur and the apparatus will not work. Alternatively a manual device 68 is provided to effect this flushing action. If flushing is not completed either automatically or manually the control unit 10 will not function further. The flow and pressure detector 15 also acts to prevent operation of the device if the pressure is above a certain critical limit, or if there is an undesired gas flow or if there is insufficient gas flow. The probe lines 55 are thus protected against damage due to excess pressure. Once the probe 12 is connected with its control unit, the gas line is connected as are the various electrical connections and the tip temperature is monitored from this time.

When it is desired to use the device the operator ac tuates the cooling cycle either by pressing the micro switch 17 on the handle of the probe or by using the foot switch 13 causing the solenoid valve 16 to open and gas to glow'to the probe.

If the gas flow is excessive the solenoid valve will be automatically actuated to prevent further gas flow. There is only one view in the unit. Should the gas flow be insufficient, the valve will be intermittently operated for some short time until either normal flow is established or if such flow is not established, the solenoid valve is again closed. The intermittent operation effectively provides a water hammer" effect which will dislodge small particles which obstruct flow in the lines.

As soon as the gas has passed through the micro orifice 62 in the probe tip a drop in temperature occurs due to the Joule-Thomson effect. The thermocouple 65 senses this temperature change and at a predetermined critical level indicates the operation of the heating coil or defrosting device 66 in the probe handle to prevent freezing of the handle and possible cold injury to the operator.

Release of the hand or foot switch shuts the solenoid valve. The defrosting unit 66 continues to operate in the handle after release of this switch until a critical temperature level is regained after the freezing process has been halted.

Should the gas pressure fall below a critical level during operation an audio visual system signals the need to replace the gas cylinder. The level chosen is such as to ensure that there is still sufficient gas in the cylinder to enable an operation to be completed.

We will now more fully describe the specific operation of the device with reference to FIG. 3 of the drawings.

When the device is connected to the gas and the power is initially turned on it is first necessary to flush the gas lines to ensure that there is no possiblity of foreign material passing to the probe preventing effective gas flow. The flushing operation can be done manually by operating a manual flush switch 68 which latches the Electro-magnetic Latching System 69 and after release of the switch the One Shot Self Locking Multi-Vibrator 70 causes actuation of the Solenoid Valve Driving Unit 71 and causes gas to flow and thus flush the lines. When the unit is initially switched on the flushing light F flashes until the latching system 69 is actuated. If the manual flush switch is not closed the Low Speed Time Base 72 acts as a clock and after a predetermined time the Electro-magnetic Latching System 69 is automatically actuated and the solenoid valve is operated. Once either the manual flush switch is actuated or the low speed time base circuit commences there is an Interlock 73 which prevents the other of these circuits becoming effective. As it is not possible to effectively flush the system whilst the probe is connected the Electro-magnetic Latching System 69 is interconnected with a Probe Sense line 75 through an OR gate 74 so that if the probe is connected the latch cannot become effective and thus the flushing light P will continue to actuate. The Probe Sense 76 may simply be a circuit to earth in the probe to indicate connection of the probe. Also, until the unit has flushed it is not desirable to permit the defrosting heater 66 in the probe to operate and thus the Electro-magnetic Latching System 69 controls a programmable voltage regulated power supply 77 from which the heater receives its power through line 78. Practically the time of flushing used may be 0.1 of a second which is sufficient time for any foreign matter to be driven from the unit. I

As the gas is connected the flow meter and pressure detector 29 described in relation to FIGS. 4 and is immediately operative as is the bridge circuit associated therewith. It is essential that if the pressure in the gas line is too high that no gas be permitted to pass because of possible damage to the lines. In order to obtain this function the output from the operational amplifier AMP 47 passes to three level detecting circuits which are Level Detector 79 for the pressure being too high, Level Detector 80 for the pressure being substantially too low and Pressure Level Detector 81 for the pressure being just too low. The output from the Level Detector 79 passes by line 82 to Gate 83 which, on receiving a signal from Level Detector 79 causes actuation through Gate 84 of a means to prevent the solenoid valve opening. At the same time the output from Level Detector 79 passes to the Gate 85 which extinguishes the pressure light P which is on when the pressure is normal. The signal from Level Detector 79 also passes to OR Gate 86 which causes initiation of a variable audible signal to indicate to the operator that there is a fault in the system. The operation of the audible signal will be described further hereinafter.

When the unit is originally switched on the High Speed Multi-vibrator 87, the AF generator 88 and the Low Speed Multi-vibrator 89 are all set into operation to provide intermittent audible and visible warning signals.

The High Speed Multi-vibrator 87 and the AF generator 88 provide the audible signals which can be applied to the loudspeaker 90 and the low speed multivibrator 89 provides pulses to operate various flashing lights, specifically the flushing light F, the pressure light P, the line block light BL and the line broken light BR.

If the pressure of the gas is just too low a signal is developed from the Level Detector 81 which passes to the Gate 91 which also has impressed thereon by line 92 the pulse train from the low speed multi-vibrator thus providing a pulsed output to Gate 85 which causes flashing of the pressure light P to indicate that the gas cylinder needs to be replaced. There is also an output from Gate 85 by line 92 to Gate 93 which provides an pulsed audible signal in loudspeaker 90. If pressure is very much too low a signal is developed from the Level Detector which passes to Gate and which extinguishes the pressure light and which also passes to OR gate 74 to the Electro-magnetic Latching System 69 which prevents this system from latching and prevents flushing by the solenoid valve.

The other output from the flow meter and pressure detector bridge is the output F through amplifier AMP 50. This output goes to two level detectors Level Detector 94 when the flow rate is higher than that which the device is calibrated and Level Detector 95 when the. flow is lower than that for which the device is calibrated. If the flow is too low and flow can only be considered when the solenoid valve is opened by the micro switch 17 on the probe or a foot switch 13, the fact that the switch has been operated is fed to AND gate 96 together with the signal from the Level Detector 95. The output from Gate 96 is passed to Gate 97 to which there is also connected a high speed multi-vibrator 98 which operates initially when the micro switch is actuated as a one shot multi-vibrator, to delay action of

gates

97, 83 and 84 for 20 milliseconds.

Normally when there is a low flow the output from Gate 96 initiates operation of Gate 97 which has a first output to Gate 99 which is an AND gate also receiving signals from the low speed multi-vibrator by line 92 and which causes flashing of the blocked line light BL. Another output from the Gate 97 to the Gate 83 to the Gate 84 and thus the solenoid valve driver unit which causes the valve to close.

On very low flow when the level detector 95 is operative before the solenoid valve is closed, there is first instituted a water-hammer effect in the probe line in order to attempt to clear any blockage which may have occurred. This effect is obtained because of an interaction between the two

transducers

40, 41. When the micro switch is closed the One Shot Multi-vibrator causes Gate 97 to open and thus the Solenoid Valve Drive Unit to open for a minimum if 20 milliseconds and there is a high gas flow into the Flow meter and Pressure Detector 29. This flow effects both the transducers thus creating an oscillatory effect trough feedback between

gates

97, 83 and 84 and the solenoid valve driving unit 71. If the flow is normal the oscillating process is over in less than 20 milliseconds and the solenoid valve remains open. If the flow is very much too low the oscillation does not occur and Gate 97 blocks Gate 83 until the micro switch is reactuated. Generally 3 to oscillations are sufficient to clear any minor blockage and this will take approximately 4 seconds. The extremely short period of operation of the one shot multi-vibrator 98 does not permit the blocked light BL to operate.

When the flow rate is too high, which normally indicates a broken line, it is essential that the solenoid valve be closed as soon as possible and the output from the level detector 94 passes to a flip flop circuit 100.

Change of state of the flip flop closes the gate 83 which in turn immediately actuates gate 84 which closes the solenoid valve. In order to reset the unit, it is necessary to provide a reset pulse at point 101 on the flip flop and the only way to provide this reset pulse is to disconnect the probe and then to reconnect the probe either after changing the probe tip or fully disconnecting the probe line, whichever is faulty. Furthermore, the change of state of the flip flop due to the too high flow with actuate gate 102 which in turn will actuate the light BR.

The operation of the micro switch 17 or foot switch 13 acts through the Gate 84 and through the Gate 103 and will only act provided the Gate 84 does not provide an absolute bar and providing that the one shot multivibrator has already acted.

The thermocouple 65 which is in the probe feeds back through a balancing circuit 104 which may be partly in the probe and partly in the control unit and the output from the balancing circuit is fed through an operational amplifier 105 to a high level current amplifier 106 to three level detectors and normally level de tector 107 acts when the temperature of the probe is below 0 C, Level Detector 108 acts when the temperature is above C and Level Detector 109 acts when the temperature of the probe reaches approximately minus 60C.

When the probe is being cooled and when the thermocouple temperature reaches below 0C, theprogrammable voltage regulated power supply 77 is connected to the heater 66 in the probe and the heater commences to operate.

As the temperature drops to below 60C, the level detector 109 operates and the cold light C is ignited. When the micro switch is released, the probe commences to heat because of the operation of the heater until when it reaches 0C the heater is disconnected and finally when the temperature reaches 20C the Level Detector 108 is actuated and the 'hot light H igmtes.

The actual temperature of the operation of the Level Detector 107 can be varied depending on the type of tip being used as it is necessary to maintain as much as possible of the tip warm whilst permitting the extreme end of the tip to become cold.

Gate 110 operates only when both its inputs are zero that is when the thermocouple measure a temperature between 0C and 20C and the output of gate 110 causes actuation of the high speed multi-vibrator 87 which in turn actuates the loudspeaker. The output from the high speed multi-vibrator is a continuous tone and indicates, in this case, the passage of the tip temperature from one state (Hot) to another (Cold) and vice-versa.

In order to prevent this tone when the probe is disconnected there is an amplifier actuated by the probe sensing device which locks operation of the high speed multi-vibrator.

As mentioned, the high speed multi-vibrator provides a continuous tone but in order to modify this, when Gate 111 is operated there is a tone which is provided by the audio frequency generator modulated by the low speed multi-vibrator.

If either the pressure is too high and/or the flow too great, the OR gate 86 will operate and this will feed through the driver 112 to the AF generator which gives an unusual and easily identifiable tone and Gate 93 will open if there is either too low a pressure and/or too low flow or if the Level Detector 80 is operating and thus Gate 85 is open. Gate 113 will only operate if there is an output from Gate 93 and the probe sensing device 76 is connected to earth, that is the probe is connected.

The output from the Gate 113 goes to an OR gate 114 which in turn goes to Gate 111 which causes operation of the loudspeaker at the modulated AF rate or the modulated AF rate as modified by the driver 112 if this is operative.

The OR gate 114 also operates if there is an output from the latching system indicating that the Flushing process has not been performed.

if the gas pressure does not reach a critical minimum this operation will not occur, as gate 74 is turned off by the level detector 80.

Should either the heater or thermocouple break down the machine will continue to operate but tone will commence warning the user of the fault. The temperature of the thermocouple causes variation in the output of the Programmable Voltage Regulator Power Supply 77 and thus the temperature of the heater in the probe.

A control switch has been inserted in the device which controls the tone transmitted. In a first position all tone is prevented, in a secondposition' only the high pressure and high flow tone, which signal the most dangerous faults, operates and in the third position all tone functions operate.

In the gas flow and pressure detector, the sensing elements which are metallic wires can be semi-conductors or crystals which have similar properties. Furthermore, the Direct Current Bias applied to the Detector could be replaced by an alternating current bias for increased stability.

1 claim:

1. Cryogenic apparatus including a control unit, a probe and switching means, the control unit being connected to a gas source whereby gas can be passed through the unit to the probe, a restricted orifice in the probe to direct gas to the probe tip to thereby effect cooling of the tip, the apparatus having control means so that the gas flow to the probe is prevented unless the gas pressure and flow rate are within predetermined limits.

2. Apparatus as claimed in claim 1 wherein the switching means operates a solenoid gas valve, the driving unit for which is interconnected with a level detector sensitive to the output of gas pressure and flow detector whereby on the gas pressure being greater or less than a predetermined maximum the driving unit is prevented from operating.

3. Apparatus as claimed in claim 2 wherein operation of the level detector also initiates the operation of a warning device.

4. Apparatus as claimed in claim 2 wherein a delay circuit is provided to prevent the operation of the level detector during a period corresponding to th e time in which the unit'is flushed.

5. Apparatus as claimed in claim 1 wherein there is provided a gas pressure and flow detector having associated with its output a level detector arranged to provide a warning on the gas pressure being slightly below a predetermined minimum.

6. Apparatus as claimed in claim 1 wherein the switching means operates a solenoid gas valve including a flushing system which must be operated before the switching means is effective including a manual flushing circuit, an automatic flushing circuit which operates when the unit is in itself actuated, a latching system controlling all other functions initiated by operation of one of the flushing circuits, operation of the flushing circuit also causes operation of the solenoid valve for a predetermined period, the arrangement being such that if the valve does not operate the latching system drops out. I

7. Apparatus as claimed in claim 6 wherein the latchtor controls a visible indication that the temperature of 12 ing system is barred from operating if the probe is attached to the control unit.

8. Apparatus as claimed in claim 6 having a warning device which operates until flushing is completed.

9. Apparatus as claimed in claim 7 wherein after completion of the flushing operation means are provided so the solenoid valve driving unit cannot operate until a probe is attached.

10. Apparatus as claimed in claim 1 wherein the probe includes a thermocouple interconnected to a first level detector in the control unit which level detecthe probe has dropped below a preselected minimum temperature.

11. Apparatus as claimed in claim 1 wherein the probe includes a thermocouple interconnected to a second level detector in the control unit which level detector controls a visible indication that the temperature of the probe has risen above a preselected maximum temperature.

12. Apparatus as claimed in claim 1 wherein the probe includes a thermocouple connected to a third level detector in the control unit, and a heating unit in the probe to prevent the probe body from freezing and to heat the probe tip when necessary, the heater being controlled by operation of the level detector at a preselected thermocouple temperature.

Claims

4. Apparatus as claimed in claim 2 wherein a delay circuit is provided to prevent the operation of the level detector during a period corresponding to the time in which the unit is flushed.

6. Apparatus as claimed in claim 1 wherein the switching means operates a solenoid gas valve including a flushing system which must be operated before the switching means is effective including a manual flushing circuit, an automatic flushing circuit which operates when the unit is in itself actuated, a latching system controlling all other functions initiated by operation of one of the flushing circuits, operation of the flushing circuit also causes operation of the solenoid valve for a predetermined period, the arrangement being such that if the valve does not operate the latching system drops out.

7. Apparatus as claimed in claim 6 wherein the latching system is barred from operating if the probe is attached to the control unit.

10. Apparatus as claimed in claim 1 wherein the probe includes a thermocouple interconnected to a first level detector in the control unit which level detector controls a visible indication that the temperature of the probe has dropped below a preselected minimum temperature.