GB2174525A - Temperature sensing alarm - Google Patents

Abstract

A temperature sensing alarm apparatus comprises means for measuring the temperature at a plurality of locations in a continual sequence. Means are included for comparing said measured temperature with upper and lower temperature values of a desired range. An alarm device is operated if the measured temperature falls out with the desired temperature range. The upper and lower temperature values at which the alarm is to be operated can be adjusted and indicators are included for indicating which of the locations initiates the operation of the alarm. <IMAGE>

Description

SPECIFICATION Temperature sensing alarm This invention relates to a temperature sensing alarm for remote temperature sensing of a plurality of locations especially but not exclusively for use in a piggery.

In certain locations it is particularly important that the temperature is restrained within accurate limits.

Thermostatically controlled heating sources can be used to achieve this but such equipment requires supervision to ensure that any failures are quickly recognised. In an environment such as a piggery the temperature must be maintained within a definite temperature band at a number of locations throughout.

To check the temperatures in such an environment manually on a continual basis is time consuming.

According to the present invention there is provided temperature sensing alarm apparatus comprising means for sensing the temperature at a plurality of locations, means for selectively measuring the temperature at each of said locations, means for comparing said measured temperature with a desired temperature value and means for operating an alarm if said measured temperature differs from said desired temperature value.

Preferably, the means for selectively measuring the temperature includes means for cyclically measuring the temperature at each of said locations in a continual sequence.

The desired temperature value may be a range and preferably means are included for altering upper and lower limits of said range.

Preferably also, means are included for indicating which of said locations initiates the operation of said alarm.

Preferably also, means are included for operating an alarm in the event of the failure of the temperature sensing or measuring means at any one of said locations.

Preferably also, there is included digital display means for displaying the temperature at each of said locations.

The apparatus may be provided with mains power supply means together with battery power supply means operable in the event of mains power failure.

Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic block diagram of a first embodiment of a temperature sensor alarm in accordance with the present invention; Figure 2 is a circuit diagram of the temperature sensor alarm of Figure 1; Figure 3 is a circuit diagram of an analogue to digital converter and display circuit of the temperature sensor alarm of Figure 1.

Figure 4 is a circuit diagram of a second embodiment of a temperature sensor alarm; Figure 5 is a circuit diagram of an analogue to digital converter and display circuit of the temperature sensor alarm of Figure 4; Figure 6 is a circuit diagram of a temperature setting circuit of the temperature sensor alarm of Figure 4; Figure 7 is a circuit diagram of the alarm triggering circuit of the temperature sensor alarm of Figure 4; and Figure 8 is a circuit diagram of the power supply of the temperature sensor alarm of Figure 4.

Referring now to Figures 1 to 3 of the drawings, a first embodiment of temperature sensing alarm apparatus comprises temperature sensors 1 connected to a 4067 16 channel analogue multiplexor integrated circuit 2 which sequentially cycles through each individual sensor channel in turn. This process is carried out by virtue of a 555 timer integrated circuit 3 which is configured as an astable oscillator and provides an output pulse at approximately ten second intervals. This pulse is applied to a 7490 4 bit decade counter integrated circuit 4 the four output lines of which assume the ten BCD conditions 00002 through to 10012 in turn before re-setting and then cycling through again.This output signal from the decade counter 4 is applied to the address input lines of the multiplexor integrated circuit 2. the multiplexor integrated circuit 2 internally decodes this input signal and thus serves to connect the input from each of the sensors 1 to a common output 5 in turn. This output 5 is fed to a display circuit 6 and to a comparator and alarm circuit 7.

The display device 6 comprises an analogue to digital converter circuit 8 which has a built in BCD to seven segment decoder suitable for driving a common anode digital display 9. Calibration controls RV1 and RV2 (Figure 3) are provided to allow the display 9 reading to be calibrated to provide a reading in C corresponding to the measured analogue voltage input.

The comparator and alarm circuit 7 comprises a d.c. preamplifier 10 which acts as a buffer before the signal is fed to one input on an upper limit voltage comparator 11 and to one input on a lower limit voltage comparator 12. The other input on each comparator 11,12 is fed from reference voltage supplies 13 and 14 which can be set by way of adjustment controls on a control panel of the apparatus to correspond to upper and lower temperature limit as desired.

Should the input signal corresponding to the temperature sensed by any one of the sensors 1 fall outside the limits of the reference voltages 13 and 14 then one or other of the comparators 11 and 12 switch state. To ensure a definite switching action the outputs from the comparators 11 and 12 are fed to Schmitt trigger circuits 15 which in turn feed the inputs of a diode OR gate 16. The output from the OR gate 16 is fed to the gate of an alarm tyristor 17.

The thyristor 17 is connected across a battery supply 18 and is in series with a a reset buttom 19 and an alarm 20.

The alarm 20 can be any suitable 12 volt device such as a hooter, siren or horn. The supply 18 can deliver up to 10 amps. A capacitor 21 is connected between the gate and cathod terminals of the thyristor 17 and, by virtue of having a suitably long time constant, prevents false triggering of the thyristor 17 due to any spurious voltage transients.

The outputs from the decade counter integrated circuit 4 are also connected to a 747141 BCD to decimal decoder integrated circuit 22. This circuit 22 serves to drive ten light emitting diodes 23 which are illuminated in turn and serve to indicate which of the temperature sensor 1 channels is being sensed. By positioning the light emitting diodes 23 next to the corresponding sensor connections on the control panel a simple indication of which channel is being sensed is provided.

When an alarm condition arises, a relay 24 is energised and serves to stop the oscillator circuit 3. This has the effect of freezing the output signal of the decade counter 4 which in turn halts the decoder circuit 22. Thus one of the light emitting diodes 23, corresponding to the channel initiating the alarm, remains illuminated for the duration of the alarm period thus indicating the alarm channel. Once the alarm has been triggered it continues in operation until the reset button 19 is pressed.

A switch 25 is included in the circuit between the oscillator circuit 3 and the decade counter 4. In conjunction with a push button switch 26 this provides the apparatus with the facility whereby it is possible to step manually through the sensor channels for the purpose of examining any individual channel. The push button switch 26 triggers a 74121 monostable 27 which provides a bounce free output pulse to the decade counter 4. The switch 25 is normally biased on so that when it is released the apparatus reverts to automatic operation.

The temperature sensors 1 which are used are three terminal devices, type LM335H, (Figure 2) and are laser trimmed to provide an output corresponding to their absolute temperature at a rate of 10 mV/ K. If any sensor 1 becomes fauly, either open circuit or short circuit, then the voltage present at the base of transistor TR1 (Figure 2) deviates from its nominal value and serves to actuate the alarm. The connecting leads to the sensors 1 are twin cored screened to prevent pick up from noise, hum, etc. Each sensor 1 is supplied through one of a series of pre-set resistors RV3-RV12 to allow calibration of the circuit for variations in lead length.

If any sensor is left unused, then a dummy piug is fitted. This consists of a 47K variable resistor connected in place of the sensor. The resistor is adjusted to give a non alarm temperature reading.

The power supply for the apparatus consists of a transformer 28 (Figure 1), the secondary of which is full wave rectified to provide a charging current supply for the battery 18. The output of the transformer 28 is also fed to a 7805 5 volt regulator 29 which suppliers the rest of the circuit. In the event of the mains supply being interrupted then the battery 18 is available to power the circuit.

The type of multiplexor integrated circuit 2 used means that it is possible to change the number of sensor channels. By substituting the 7490 counter 4 with a 7493 4 bit binary ripple counter the apparatus can be configured to provide an eight channel or sixteen channel counter.

In use the upper and lower temperature limits desired can be set and the apparatus then allowed to operate providing a continuous cyclic digital readout representing the temperature at each sensor 1 in turn. Should the temperature at any sensor 1 fall outwith the desired limits then the alarm will be acutated.

The apparatus is particularly suitable for use in the environment of a piggery when the lower and upper temperature limits for initiating an alarm condition are in the ranges 0 C to 200C and 20"C to 40 respectively.

The apparatus has a number of important features. The channels are automatically sensed at 10 second intervals. The sensors may be situated up to 100 metres from a central control unit. A battery supply is provided as a backup in the event of a mains power failure. The alarm operates in the event of a sensor failure. Automatic identification of the channel which initiates an alarm is provided. The apparatus requires no maintenance other than periodic checking of the battery.

Referring now to Figures 4 to 8 of the drawings a second, improved, embodiment of temperature sensor alarm apparatus is illustrated. Table 1 lists the part numbers and values of the numbered components on Figures 4 to 8 of the drawings.

TABLE 1 ltem Description Item Description R1/R16 0.25W Metal Film 1% 1K C15 POLY 470nF R17 0.25W Metal Film 1% 150R C16 ELEC 25v 100uF R18 0.25W Metal Film 1% 1K C17 POLY 220nf R19 0.25W Metal Film 1% 150K C18 POLY 470nF R20 0.25W Metal Film 1% 1K5 C19 POLY 220nF R21 0.25W Metal Film 1% 15K C20 ELEC 25v 4700uF BR22 0.25W Metal Film 1% 47K IC1 4067 R23 0.25W Metal Film 1% 680K IC2 4516 R24 0.25W Metal Film 1% IM IC3 4514 R25 0.25W Metal Film 1% 470K IC4/5/6 4050 R26 0.25W Metal Film 1% 2K2 IC7 74121 R27 0.25W Metal Film 1% 100K IC8 555 CMOS R28 0.25W Metal Film 1% 150R IC9 7107 R29-R42 0.25W Metal Film 1% 15K IC10/11 78C915 R43-R56 0.25W Metal Film 1% 470R IC12/13 4585 R57-R72 0.25W Metal Film 1% 47K IC14/15 4585 R73 0.25W Metal Film 1% 100K IC16 4081 R74 0.25W Metal Film 1% 2K7 IC17 4072 R75/76 OR68 11w D1-D16 5mm 20mA LED R77/R78 0.25W Metal Film 1% 4K7 D17 lCL 8069 VR1/VR16 18 TURN CERMET 10K D18 IN4001 VR17 18 TURN CERMET 10K 500K D19 3ZO1.3W VR18 18 TURN CERMET 10K 50K TR1 BC109 C1 TANT 1uF TR2/15 BC327 C2 CER i0nF TR16 BC109 C3 TANT 10uF Q1/2/3 7805 C4 POLY 0.22uF S1-S16 LM335Z C5 POLY .047uF Disp. 1 0.56"7SEG. & /-1 C6/C7 CER i0nF TH 1 TIC 126D C8 POLY 100nF BR1 10 AMP.METAL CLAD C9 CER 100pF RL 1 i2vDC SINGLE POLE C10 ELEC. 10v 47uF TX 1 2.12v 25VA C11 ELEC. 10v 100uF M 1 5AMP.MOVING IRON C12 ELEC. 16v 4700uF SW 1 SPCO ONE WAY BIAS C13 CER 56pF SW2/3/4/5 BCD 0-9 C14 POLY 220nF SW6/SW7 SPST The operation of this embodiment is in most respects similar to the embodiment described in relation to Figures 1 to 3.

Referring to Figure 4 the inputs from the temperature sensors are connected to YO to Y15 of IC1. The temperature sensors used are of a three terminal semi-conductor type whose output varies linearly at 10mV per degree Kelvin. Variable resistors VR1 VR16 are used for calibration purposes to trim out errors due to the variations in resistance of leads of different lengths. IC1 is a 16 channel multiplexor and cycles through each channel in turn, stopping at each location for approximately 5 seconds. This is achieved by using a 555 timer (IC8), which is configured as an astable oscillator.The output pulses from the 55 are fed to IC2, which is a binary up and down counter whose four output lines 00 to 03 are connected to the address lines Al to A3 of IC1. Each temperature sensor input to IC1 is thus sequentially connected to the output Z of IC1. This signal is then fed to an analogue to digital convertor IC9 (Figure 5). The output lines of IC2 are also fed to IC3 which is a 1 of 16 decoder, to provide a signal to identifying LED's D1 to D16 for each of the temperature sensors. The LED drives are buffered by IC4, IC5 and IC6.A switch SW1 is included in the circuit between the 555 oscillator and the binary up and down counter IC2. In conjunction with a push-button switch PB1, this provides the apparatus with the facility whereby it is possible to step manually through the sensor channels for the purpose of examining any individual channel. Depressing PB1 triggers a mono-stable IC7 which provides a bounce free output pulse to the binary up and down counter IC2. SW1 is biased to AUTO, so that when it is released the apparatus reverst to automatic operation.

Referring to Figure 5, the segment outputs for the units and tens are fed to the level shifter transistor stages TR2 to TR15 which provide positive true logic signals for the alarm circuitry. These signals correspond to zero voltage when the relevant segment is off and +5 volts when the segment is on. The segment voltages are fed to IC10 and IC11 (Figure 6) which are seven segment to BCD convertors. The next stage of the alarm consists of four comparator IC's, IC12, IC13, IC14 and IC15. Each of these IC's has two separate four line BCD inputs. One input is from IC10 or IC11 and the other input is from one of four thumbwheel switches, SW2, SW3, SW4 and SW5, which are used to set the temperature limits on the front panel manually.As shown in Figure 6 word A is considered to the BCD input from either the units or tens of the seven segment display. Word B is taken to be the BCD voltages set up by the thumbwheel swtiches. The resultant outputs from the four comparators IC12 to ICIS will provide the following conditions.

Upper units A=B Lower units A=B A > B A < B Upper tens A=B Lower tens A=B A > B A < B The following logic conditions are necessary for satisfactory operation of the alarm.

LO HI Tens Units Tens Units (A=B) (A=B) (A=B) ~~~~~~~~~~ ~ (A=B) (A=B) (A < B) (A=B) (A > B) A < B A > B The above functions are carried out by the quad two input AND gate IC16 and the dual quad input OR gate IC17.

The trigger signal from pin 13 of IC17 is fed to a transistor stage TR16 (Figure 7) where the components R73 & C10 provide a delay of apploximately 2 seconds before firing the thyristor TH 1. This overcomes the problem of faise triggering due to mains transients and the like. When the alarm is activated, RL1 becomes energised which feeds 12 volts back to TR1 in the oscillator stage of the multiplexor. This stops the oscillator at that instant thereby providing automatic identification of the channel which initiated the alarm condition.

The power supply (Figure 8) consists of transformer TX1 the secondary of which is full wave rectified by BR1. This provides a suitable voltage for charging a back-up battery, the current being fed through R75 and R76 to provide a trickle charge and M1 which is used to indicate the battery charging current.

The rectified output is also fed to Q1 and Q2 which provide a double stage of DC regulation, the resultant smoothed 5 volt output is used to supply the digital display IC9. A further regulator stage Q3 is used to provide +5 volts for the remainder of the integrated currents. lC9 acts as an analogue to digital convertor and provides suitable signals for driving a common anode seven segment display. VR17 and VR18 are used to calibrate the span and scale factor. A high precision voltage reference D17 is employed to give greater accuracy.

If any sensor position is left unused, and the temperature at that position is likely to fall outside the upper or lower limits set by the thumbwheel switches, then dummy plugs can be fitted in the relevant sockets. These consist of a 1K fixed resistor and a 1K variable resistor is series mounted in a 3 pin DIN plug. The variable resistor is adjusted to give a non-alarm reading. The alarm system is an active device insofar that should any sensor or sensor cable become damaged, either open circuit or short circuit, then the alarm will go off.

Modifications and improvements may be incorporated without departing from the scope of the invention.

Claims (8)

1. Temperature sensing alarm apparatus comprising means for sensing the temperature at a plurality of locations, means for selectively measuring the temperature at each of said locations, means for comparing said measured temperature with a desired temperature value and means for operating an alarm if said measured temperature differs from said desired temperature value.

2. Temperature sensing alarm apparatus as claimed in Claim 1, wherein the means for selectively measuring the temperature includes means for cyclically measuring the temperature at each of said locations in a continual sequence.

3. Temperature sensing alarm apparatus as claimed in Claim 1 or 2, wherein the desired temperature value is a range and means are included for altering upper and lower limits of said range.

4. Temperature sensing alarm apparatus as claimed in any one of the preceding Claims, wherein means are included for indicating which of said locations initiates the operation of said alarm.

5. Temperature sensing alarm apparatus as claimed in any one of the preceding Claims, wherein means are included for operating an alarm in the event of the failure of the temperature sensing or measuring means at any one of said locations.

6. Temperature sensing alarm apparatus as claimed in any one of the preceding Claims, wherein digital display means are included for displaying the temperature at each of said remote locations.

7. Temperature sensing apparatus as claimed in any one of the preceding Claims, wherein the apparatus is provided with mains power supply means together with battery power supply means operable in the event of mains power failure.

8. Temperature sensing apparatus substantially as hereinbefore described with reference to the accompanying drawings.