EP0268649A1

EP0268649A1 - Breath alcohol or drug detecting device

Info

Publication number: EP0268649A1
Application number: EP19870903735
Authority: EP
Inventors: Thomas Parry Jones
Original assignee: Lion Laboratories Ltd
Current assignee: Lion Laboratories Ltd
Priority date: 1986-06-14
Filing date: 1987-06-12
Publication date: 1988-06-01
Also published as: AU7487687A; GB8614514D0; WO1987007724A1

Abstract

Un dispositif, permettant de mesurer ou de détecter la présence ou la proportion d'alcool ou de stupéfiants dans l'haleine expirée dans l'atmosphère, comprend un instrument tenu à la main comportant un détecteur d'alcool ou de stupéfiants ou une pompe permettant de prélever un échantillon de gaz dans l'atmosphère et de l'introduire dans le détecteur par une ouverture d'entrée, le détecteur étant conçu pour détecter une faible proportion d'alcool ou de stupéfiants dans l'échantillon. Ledit détecteur envoie également un signal de sortie à une unité d'enregistrement ou d'affichage contenue dans l'instrument, celui-ci comportant en outre un dispositif lumineux clignotant électrique comprenant un élément émetteur de lumière, une batterie et un commutateur d'actionnement.A device for measuring or detecting the presence or proportion of alcohol or narcotic drugs in breath exhaled into the atmosphere, comprises a hand-held instrument comprising an alcohol or narcotic detector or a pump for take a sample of gas from the atmosphere and introduce it into the detector through an inlet opening, the detector being designed to detect a small proportion of alcohol or narcotic drugs in the sample. Said detector also sends an output signal to a recording or display unit contained in the instrument, the latter further comprising an electric flashing light device comprising a light emitting element, a battery and an actuation switch .

Description

"Breath Alcohol or Drug Detecting Device"

This invention relates to an alcohol or drug breath detecting device intended for use without the voluntary co-operation of the person being tested. The invention is thus particularly applicable for use by the police in checking suspects, especially vehicle drivers, for drunken driving offences.

Conventional breath testing instruments require that the suspect should breath into a tube from which a gas sample is taken, but the invention ' is based on the appreciation that a valuable indication of alcohol or drugs content in the breath can be achieved without the limitations of such previous^' systems.

One of the objectives of the invention is to provide an instrument which will enable a police officer to obtain a useful assessment of whether a driver has consumed alcohol or drugs without the need for conducting a formal official breath test which has a number of related problems and disadvantages both for the police and for the suspect driver. The invention is based on the discovery that a reasonably accurate breath alcohol test can be made by using a specially designed instrument spaced from the mouth of the suspect, while the suspect is breathing out or speaking. To do this the alcohol detector must be extremely sensitive and specially designed and there must be an effective specially designed sampling system and evaluation circuit. It is also of advantage to include means to ensure that the sample is taken at the correct position in relation to the suspect's mouth.

Now broadly stated the invention consists in an instrument for measuring or detecting the presence or proportion of alcohol or other drug in breath expired int the atmosphere, including a hand-held instrument comprisin an alcohol or drug detector, a pump for drawing a sample o gas from the atmosphere through an inlet opening into the detector, the detector being arranged to detect a small portion of alcohol or drug in the sample, and to provide α tput to a recording or display unit in the instrument, the instrument also including an electric flashlight havi a light radiating element, a battery and an operating switch-. Preferably the gas inlet opening is positioned adjacent to the light emitting part of the flashlight, and in a particular preferred construction it is positioned on one side of the body of the flashlight. For example, the detector may include a display unit on one side of the body of the flashlight with the gas inlet opening on another side of the body. This positioning of the components enables the police officer to operate the instrument conveniently without the suspect being aware that an alcohol breath test has been taken. It is normal for a police officer to shine a flashlight into a vehicle through the driver's window and normally the beam of the flashlight is directed across the vehicle in front of the driver's face. In this position the driver's mouth will be reasonably close to the inlet opening on the side of the flashlight and at the same time the police officer can examine the display on the top of the flashlight body.

, To assist in thi's proper positioning, which in the preferred embodiment of the invention is approximately 15 cm between suspect's mouth and inlet opening, the instrument preferably includes a proximity detector or range finder to assist in locating the drug or alcohol detector in the correct position for a test. For example, the instrument may include an optical range finder comprising one or more focused beams of light, or it may comprise a pulsing acoustic transmitter and receiver and means for assessing the echo interval.

In any case the alcohol detector preferably includes an electrochemical fuel cell with an electrical amplifier and evaulation circuit and in order to prepare the instrument as rapidly as possible for another test the instrument preferably includes means for short circuiting the electrochemical cell during intervals between alcohol or drug tests.

The sampling pump may be of various different types but in a particular preferred construction it is electrically acutated and includes a timer for determining its running time. ^■ Alternatively the pump may be manually operated in conjunction with an operating spring and a trigger or latch such that the spring can be quickly loaded, nd released by a trigger to draw in a sample of gas when required. The electrically operated pump, however, has the advantage of being able to draw in a large volumetric sample which is of advantage when sampling breath at some distance from the suspect's mouth. The alcohol detector also preferably includes an alcohol high level limit sensor and a warning device actuated in response to a detected high alcohol level and according to a preferred feature of the invention the alcohol detector includes an illuminated alcohol level display and also means for dimming this display when the flashlight is operated. The invention may be performed in various ways and one particular embodiment with some possible modifications will now be described by way of example with reference to the accompanying drawings, in which:-

Figure 1 is a simplified diagram illustrating a combined flashlight and breath detector according to the invention,

Figure 2 is a component circuit diagram illustrating the electrochemical cell and detector circuit,

Figure 3 is a cάrc'uit diagram illustrating a further component of the circuitry including threshold comparator and flashing display, Figure^' 4 is a further circuit diagram illustrating a heater control and temperature indicator circuit,

Figure 5 is a partial circuit diagram illustrating a battery condition tester, Figure 6 is a circuit diagram illustrating the circuitry controlling the sampling pump,

Figure 7 is a simplified block schematic diagram illustrating the sequence of operation of certain electronic switches, Figure 8 is a table illustrating the sequence of switch positions of the circuitry of Figure 7,

Figure 9 is a side elevation partly in section illustrating the sampling pump, motor, and electrochemical cell,

Figure 10 is a diagrammatic plan view of the cell,

Figure 11 is a diagram partly in section illustrating an optical range finder system, and

Figure 12 is a similar illustration of an ultrasonic range finder system.

In the example illustrated in Figures 1, 9 and 10,the instrument comprises a casing 10 which contains a torch or flashlight and the alcohol breath detection system, and a hollow handle 11 which acts as a compartment for batteries. The casing 10 has an opening at the front end 12 covered by a transparent lens to allow the beam of the flashlight to project forwards on the central axis 13 and on the top of the casing in the position shown in Figure 1 there are two switches 14,15, switch 14 being arranged to switch on the beam of the flashlight, while switch - 15 energises the alcohol detector system. In addition there is a digital display panel 17 containing a conventional L.E.D. digital display to indicate the alcohol content of the sensed breath in the usual units of milligrams per litre. The display panel also has two indicator lights LI and L2, L2 being arranged to indicate that the detection system is ready for use while Ll indicates that the battery voltage is below standard.

The casing is also formed with a small inlet 20 on the left-hand side, as seen in Figure 1. As will be explained this is appropriate for tests on a vehicle driver where regulations require driving on the right-hand side of the road.

In order to test for alcohol breath content the flashlight will be held with the inlet 20 at the appropriate distance from the suspect's mouth and while the suspect is speaking a small sampling motor 25 is actuated by the switch 15 to draw a breath sample into the alcohol detection unit. The pump unit is illustrated in Figure 9 and includes a miniature electric motor 25 driving an eccentric crank 26 connected by a bushing and rod 27 to a flexible membrane 28 within the diaphragm pump chamber 29. The space below the diaphragm communicates via a port 30 with the chamber 31 above the electro¬ chemical fuel cell 32. N.on-return valves not illustrated) -prevent return flow so that oscillation of the diaphragm causes gas to flow through the instrument from the inlet 34 to the outlet 35. The inlet tube 34 is connected to the entry port 20 on the side of the flashlight and the port 35 is connected to a vent. The space 37 below the cell 32 is permanently vented to atmosphere,or exposed to ai Thus after the motor has run for a predetermined period of, say, 4 seconds a sample of the suspect's breath will be contained within the chamber 31 above the cell 32 and the chamber 37 below the cell will be open to atmosphere and accordingly the cell will develop a current and voltage related to the alcohol content of the breath sample. To prevent excessive condensation in the instrument small heater 40 is mounted on a heater disc in the cell chamber and a temperature sensing thermistor 41 positioned also in the chamber in thermal contact with the disc is connected into an automatic temperature control circuit. A number of alternative sample pumping systems are possible. or example, there may be a piston type sampling pump operated manually or by means of a pre-loaded spring with a manually operated trigger or release latch.A piston o plunger type pump of this nature will only draw in a small volumetric sample and accordingly the alcohol detector circuit needs to be extremely sensitive.By comparison the electrically operated sampling pump will draw in a much larger volume which.is of considerable advantage when detecting breath alcohol in the open atmosphere.

The electrical circuits incorporated in the instru¬ ment are illustrated diagrammatically in Figures 2,3,4,5,6 & 7. igure 2 illustrates the amplififer circuit between the fuel cell 32 and an integrated circuit element 45 acting as a microprocessor to control the L.E.D's of the three digit display units 46,47,48.Figure 3 illustrates a threshold comparator circuit and also a flashing display circuit and an increment circuit.Figure 4 illustrates the heater and thermostat temperature control circuit while Figure 5 illustrates the battery voltage circuit.Figure 6 illustrate the part of the circuit controlling the operation and timing of the sampling pump motor and Figure 7 is a schematic diagram illustrating the components of the basic logic circuit. Referring to the circuit diagrams of Figs.2 to 7, when switch SW2 is in ON position the gate of FET Ql is biass

ON and Ql is conducting. In this condition the output of the fuel cell 32 is across R45 and QS of Ql so that the amplifier"sees"the output of the fuel cell across the combined resistance. Before a sample is taken this is the zero condition for the fuel cell and amplifier. After sample has been taken when SW2 is returned to ON position, the fuel cell discharges across this low resistance allowing the operator to observe the fuel cell recovering as display recovers to zero.

When SW2 is in "SAMPLE" position the output of the fuel cell output developed across R2 is applied to one input of operation amplifier 51 which is connected as a non-inverting amplifier. The feedback network consisting of R3 and R4 (calibration pot) determine the gain, and R5 provides an offset null adjustment for Si while R4 varies the gain of 51, therefore varying the output from Amp 51 which goes to the Integrated Circuit Unit 45 (ICL 7107) acting as an analogue/digital converter. 51 also has an adjustable precision reference buffer which consists of a reference voltage source of 200 mV to the input of the reference amplifier. Feedback is applied to 55 which controls the reference output at 56 and this feedback network consists of R7 and R6 and fixes the output at 2.2 volts. This 2.2 volt reference is applied at several points in the circuit as will be explained hereafter.

The A/D converter 54 is a high performance low power converter containing all the necessary active devices on a single CMOS-IC. Included are seven segment decoders, display drivers,a reference, a clock 65, and auto-polarity and auto-zero circuitry. This allows direct interfacing with 7 segment common anode LED displays. The basic components are illustrated diagramatically in Figure 7 and the equivalent electronic switch positions are shown in Figure 8.

The IC 54 utilises the dual ramp principle in which the unknown input voltage is used to charge a capacitor for a fixed time. Then with the unknown disconnected, a reference voltage is used to discharge the capacitor. The time taken to discharge the capacitor is a measure of the unknown voltage. To ensure that the charge and discharge are linear an integrator is used.

Signal conversion consists of three operational phases; during the first the I.C. goes through an internal zeroing sequence and in this way an applied zero input voltage will be guaranteed to give a display reading of zero. During the second phase the I.C. integrates the applied signal voltage for a fixed time and in the third phase de-integrates this result using an applied reference voltage and timing this process. The time required is proportional to the applied signal voltage. Specifically, the digital reading display is:-

1000 x V IN

V REF

The reference voltage is input on terminal 56 with respect to terminal 60, and is provided by the potential divider resistors Rll and R12. The signal voltage is input on terminal 62 with respect to terminal 56. The reference voltage is 1.1V so that a digital reading of 100 will be given by a signal voltage of HOmV. Initially the control logic sets the electronic switches as shown in the table of Figure 8. In this mode the unknown input is applied to the integrator, comprising amplifier 56, Rl and Cl, via buffer amplifier 57. The integrator output therefore ramps positively or negatively, depending on the input polarity, for a period set by the internal clock oscillator. At the end of this period, state 2 is selected and the input is disconnected and the positive or negative reference connected to the integrator which subsequently begins to ramp towards zero. The comparator 58 determines, during the initial ramp, which reference is selected and also detects that state of zero integrator output. During state 2 the counter 59 accumulates clock pulses until the integrator reaches zero, i.e. comparator 58 changes state. At this point state 3 is selected: here the accumulated count and polarity are displayed giving the unknown input value and the auto-zero mode is selected, which short circuits the input and connects capacitor C2 between the buffer amplifier 57 output and short circuited integrator and comparator. Auto- . zero capacitor C2 thus charges to a value determined by the offsets appearing at the amplifier outputs and the period of the auto-zero mode; this timing is once again determined by the clock oscillator .65. Upon completion of auto-zero, state 1 is reselected and thus the whole cycle is repeated. However, the charge on the auto-zero capacitor C2 is subtracted or added to the input voltage thereby correcting any drift in circuit performance. In the event of an input not being applied the auto-zero mode maintains a zero reading by continuous compensation of amplifier drift. The reference voltage (2.2 volts) on terminal 56 is divided down across Rll and R12, so that voltage at Pin 60 of the A/D converter 54 is 1.1V. The threshold circuit, which causes the display to flash when a certain alcohol level has been exceeded, is controlled by the output of comparator 61. This has one inverting input connected to the reference voltage provided at terminal 56 of 55 and is set at 2.2 Vdc.

The other non-inverting input is connected to the output of the amplified fuel cell signal on 62 via a potential divider consisting of R8 and R9. The output 64 of the comparator 61 remains low -(OV) -until the non-άnverting input voltage from 62 exceeds^■ the 2.2 Vdc on 56. .(This occurs when display-^- 100) . When voltage on 56 < input 62, output 64 goes high (6V) and remains there until voltage on 62 drops to a predetermined value (this occurs when display 060) . This hysterisis in switching the comparator output from high to low is achieved by the feedback resistor R38 feeding a proportion of the output back to the non-inverting input so holding it high after .fuel cell output has dropped below initial crossover voltage.

As long as output 64 of 61 is low (OV) the base of Q2 is at ^ 5.4 V, that is 0.6V below the emitter voltage, and this will bias Q2 ON. With Q2 ON (conducting) the common anodes of the displays are connected to the positive voltage rail in either of two conditions.

(i) Directly through Q2 and SW1 to full voltage rail (6V) , when SWI is in OFF position (i.e. Torch/Flashlight OFF) . (ii) Through zener diode CR1 and Q2 to 6V supply.

When SWI is ON position (i.e. Torch/Flashlight ON) , the voltage to the Emitter of Q2 is set at 2.4V by CRl and the base is at 1.7V. The result is a dimming of the display because of the lower anode voltage of 2.4V.

When terminal 64 goes high ( 6V) , the base of Q2 also goes high. This will initially turn Q2 OFF, but the base of Q2 is connected to input of U5 (2/2 of 7556) via R24 and CR3. This half of U5 is connected as an astable multivibrator. The base of Q2 wil now follow the voltage at the input of U5, and this results in the display flashing OFF when the input goes high and ON again when the input goes low. LED L2 and the heater circuit are operated by comparators 71, and 72 respectively. -The temperature sensor is a thermistor 41 which forms a potential divider with R36 the two being between V⁺ (6v) and earth. The voltage at the junction of the thermistor and R36 forms the variable input to the inverting inputs to the two respective comparators 71,72. The two remaining inputs to these two comparators are the no inverting reference inputs. One of these is kept approximately 100 mV below the other, which allows the heater circuit to cycle ON and OFF, maintaining the correct temperature, without the LED circuit being operated every time the heater comes on. This ensures that the LED L2 is ON only when SW2 is initially switched on from cold. During normal operation, as long as SW2 is ON or SAMPLE position, L2 should not normally be illuminated, unless the device is used in a particularly cold environment. When the heater is ON the output 73 of 72 is high ( 5.0V), and this is applied to the gate of Q3 turning it ON, so connecting the heater to earth and switching the heater ON. The LED L2 is On when the output 74 of 71 is high ( 3.6V).

If V⁺ = 6.0V (i.e. fully charged batteries) at 25°C, the junction voltage of thermistor and R36 is 3.12V: this is greater than the voltage inputs 71 and 72 on opposite sides of R33, and in this state both comparators will have the outputs low, i.e. L2 OFF and HEATER OFF. As the thermistor cools, the junction voltage falls, until it drops below V ref of the input to 72 so that output 73 goes high switching ON the heater. In this way the heacer will operate before the L2 comparator operates to illuminate L2 .

Both comparators have feedback resistors - R31 and R35 so that a degree of hysteresis is introduced to the comparator switching. To indicate a low battery voltage, the LED Ll is connected to output 75 of 76 (2/4 of U2) . The non- inverting input is connected to the junction of R22 and R23 which forms a potential divider chain between V+ (battery voltage) and earth. The inverting input is connected to the 2.2V reference voltage supplied by terminal 56 of 55.

When the battery 1 voltage is greater than 4.V, the voltage at one input of 76 is 2.2V and the output at 75 is kept high and Ll is OFF. When the other input is 2.2V (battery voltage < 4V) the output at 75 will' swing low and the voltage drop across Ll through R21 switches Ll ON.

The sampling pump is controlled by a circuit illustrated in Figure 10, which includes 81 (1/4 U4) 82 ( h U5) (Q4) and (Q5) (JFET Transistor Switches) . It is operated when SW2 is pushed to "SAMPLE" position. Pin 1 of 81 is one input of an EX OR, is taken from high to low, so the output, at 83, switches from high to low. This high to low transition is "differentiated" by capacitor C8 into a sharp negative going spike which is applied to input 85 of 82 (h 7556) . This negative going spike initiates the mono-stable timer 82 so that the output 86 goes from low to high for appoximately 4.5 sec: the length of this transition is set by R29 and C7. When 86 goes from low to high it will bias the gate of FET Q5 ON,thus connecting the pump motor 25 to ground and switching it ON. PNP transistor Q4 is acting as a constant voltage source derived from the 2.2V reference voltage on 56 and capacitor C9 provides transient suppression when the pump is being switched.

It is important that when testing a suspect the instrument should be positioned quite accurately at the correct distance from the suspect's mouth. In this example the inlet port 20 is positioned on the left-hand side of the flashlight casing when the display panel is uppermost and visible to the police officer.In use the instrument will be held with the beam of the flashlight directed across the vehicle in front of the suspect and the object then is to position the inlet at approximately 15 cm from the suspect's mouth at the time when he speaks.

Accordingly in the example illustrated in Figure 11, an optical range finder system is incorporated in the instrument.This comprises a miniature optical projector unit 90 deriving light from the main bulb 91 of the flashlight by way of a small opening in the parabolic reflector cone 92. The projector unit is arranged to direct a focussed beam of light laterally and the focussing is such that the beam is concentrated to a small spot at a distance of 15 cm from the side of the flashlight where the inlet is located.Thus in use the police officer aims the flashlight across in front of the driver's face, presses the switch to illuminate the flashlight and then observes the small light disc which appears on the suspect's face. By moving the flashlight towards and away from the suspect's mouth the disc can be made to contract to a spot, at which point the distance is correct and the sampling switch can be pressed to take an alcohol breath reading.

In the alternative embodiment illustrated diagrammatically in Figure 12 an acoustic range finder device is incorporated in the instrument comprising a small ultra-sonic transmitter 95 coupled with a receiver 96 and connected into electronic circuitry which in itself is well-known for establishing the time interval between a pulse transmitted and the reflected pulse derived from reflection of the sound wave off the suspect's face. The time interval is converted into the respective range which may be displayed digitally: for simplicity and convenience it is preferred that the circuit includes high level and low level comparators and two coloured lights respectively, indicating hi'gh or low, i.e. too far or too close, such that the correct range is obtained with both lights illuminated. In lieu of a range finder system a proximited detector may be incorporated, for example an inductance or compacitance type proximity detector of known design coupled with an oscillator circuit arranged to produce an output when the proximity detector is within a predetermined distance (say 15 cm) from the head of the suspect. A small light or other indicator on the body of the flashlight will indicate that the proximity detector has been triggered. To operate the instrument so as to take a sample, without the flashlight on, first push the electronics switch (SW2) to the On position. Ll LED "Battery Low" should remain OFF: if it illuminates batteries require changing. L2 heater will normally illuminate for up to 60 sec: do not proceed to sample until this LED is OFF. The digital LED display should read zero, and if not should be adjusted to zero.

To take a sample push electronics switch (SW2) to SAMPLE position and hold the sample inlet port approximatel 6" (15 cm) from subject's mouth while subject is talking. The Digital Display will increment in units of 5,. until a peak reading is reached after approx. 30 sec (depending on alcohol concentration) . If the indicated alcohol level is greater than 100 the display will start to flash on and off to draw the operator's attention to the relatively high alcohol reading.

If flashlight is required push flashlight switch (SWI) to ON position. In this position the intensity of the display LED's (not indicators Ll and L2) will drop to approximately 50% of intensity with flashlight off.This is to conserve power: also use of the flashlight infers night time use when intensity of display required is not as high as during day time use.

With electronics switch (SW2) in ON position _Q6 and Q7 are biased ON. With Q7 conducting, an earth current path is created for the electronics system thus applying correct operating voltage to all electronic components and switching them ON. Ql is biased ON, ' thus shorting the fuel cell output across R45: this is a virtual short circuit which discharges the fuel cell, and results in 000 display. The heater circuit will operate via IC's Q2 and Q3 and associated circuitry and LED L2 will appear for a short period whilst sample system is brought up to temperature: at correct temperatur L2 is OFF. Also now operating is battery low LED Ll via 76 (U2) and potential divider chain (R22, R23) . Also with electronics switch in ON position IC's 51,91 (7556 timer) 54- (A/DLED driver) and associated components are powered at correct voltages.

51 provides a reference voltage of 2.2 Vdc with respect to ground which is used as the reference voltage of 54 (7107) as well as reference voltages for several inputs to IC, 72. When electronics switch SW2 is in SAMPLE position, Ql is biased OFF and fuel cell output is across load resistor R2 so that output is amplified by 51, output of 51 is adjusted by R4 and fed on 62 to 54 for display on LED display. The sample is drawn across the fuel cell by the miniature pump. The pump sequence starts when SW2 is put into SAMPLE position 82 (7556 timer) is activated and biases Q5 ON so that voltage is applied to pump for approximately 4.5 &ecs. The output of the Op Amp 51 as well as being applied to 62 of the I.C 54 is also applied to one input of 61 via R8. When voltage at this input exceeds the other input the output 64 goes high, and this brings in the circuit consisting of 91 (h 7556 timer) , CR3, Q2 and causes display to flash, drawing the attention of the operator to the reading. Switching On switch SWI (flashlight) activates the flashlight bulb via R46. This also switches supply to LED Display across zener Diode CRl and this drops the intensity of display.

It will be appreciated that the invention can be applied to the detection of drugs such as marijuana in breath samples by substituting an appropriate drug detector for the electro-chemical alcohol-activated fuel cell 32.

Claims

1. An instrument for measuring or detecting the presence or proportion of alcohol or other drug in breath expired into the atmosphere, including a hand¬ held instrument comprising an alcohol or drug detector, a pump for drawing a sample of gas from the atmosphere through an inlet opening into the detector, the detector being arranged to detect a small proportion of alcohol or drug in the sample, and to provide an output to a recording- or display unit in the instrument, the instrument also including an electric flashlight having a light radiating element, a battery and an operating switch.

2. An instrument according to Claim 1, in which the gas inlet opening is positioned adjacent to the light emitting part of the flashlight.

3. An instrument according to Claim 1 or Claim 2, in which the gas inlet opening is positioned on one side of the body of the flashlight.

4. An instrument according to Claim 3, in which the detector includes a display unit on one side of the body of the flashlight with the gas inlet opening on another side of the body.

5. An instrument according to Claim 1, in which the alcohol or drug detector includes an electro- chemical fuel cell with an electrical amplifier and evaluation circuit.

6. An instrument according to Claim 5, including means for short circuiting the electrochemical cell during intervals between tests.

7. An instrument according to Claim 1, in which the pump is electrically actuated and includes a timer for determining its running time.

8. An instrument according to Claim 1, in which the detector includes a high level limit sensor and a warning device actuated in response to a detected high alcohol or drug level.

9. An instrument according to any of the preceding claims, in which the detector includes an illuminated level display -and also means for dimming this display when the flashlight is operated.

10. An instrument according to Claim 1, including a proximity detector or range finder to assist in locating the detector in the correct position for a test.

11. An instrument according to Claim 7, in which the instrument includes an optical range finder comprising one or more focused beams of light.

12. An instrument according to Claim 7, in which the proximity detector comprises a pulsing acoustic transmitter and receiver and means for assessing the echo interval.