# Digital Temperature Indicator Circuit

This explained digital temperature indicator circuit had been created for computing the heatsink temperature of a big over 1kva power amplifiers, however it may, obviously, be applied for other power amplifiers and even for various other purposes.

The thermometer would not just display the heat range of the heatsink on a couple of displays, nevertheless additionally, it offers a switched output that, for example, may be used to switch on a fan in case the heat goes up over a pre-determined level.

The proposed digital temperature meter circuit includes four parts: a reference voltage origin, IC1, the sensor, IC4, the display segment, IC2 as well as IC3 and also the switch portion, IC5. IC1, a 723, offers a stable source voltage for the sensor and switch area. This voltage is around 8 V. The temperature sensor gives a temperature based voltage of 10mV/K. At 0°c, as an illustration, the voltage around IC4 sums to 273 X 0.01 = 2.73 v (0° c = 273 K)

The display screen area is built around a couple of good old faithfuls: lCs CA 3161E and CA 3162E. lC2 includes the A/D converter as well as the multiplexing circuit for the displays. IC3 may be the BCD seven-segment decoder driver. Just a couple of displays are employed, in order that the temperature could be examined in degrees.

lC2 reads the variance between the voltage offered by the sensor and also the reference voltage established by pot P 1.

This really is recommended to get rid of the ‘273 degrees under 0’, that is, the particular voltage of 2.73 V. For making this achievable, the read-out section and the measuring/switching segment are driven independently.

The negative of lC2 and lC3 is attached to the wiper of P1 that is at a potential of 2.73 V, whilst the input of ‘meter’ lC2 is actually linked to sensor IC4. ln this particular method, the 2.73 V is reimbursed in order that the voltage assessed by lC2 goes up at 10 mV per degree centigrade from 0° C and the exhibits degrees centigrade. The very last, although not least, section of the circuit is the comparator and switching output (IC5 and T3).

The voltage given by the sensor is when compared by IC5 using a voltage extracted by R9 and R10 from the reference voltage of lC1. Once the sensor voltages increases over this supplementary reference voltage, the outcome of IC5 alterations status and the transistor conducts.

T3 can easily, for example, using a relay switch on a fan to deliver further cooling to the power transistor. It is furthermore feasible to switch off the sound system through the safety relays in the amplifier, to ensure that the dissipation in the power transistors is significantly lowered, supposing, obviously, that the loudspeaker operation caused the the overheating!

Together with values of R9 and R10 as demonstrated, the comparator alters status at about 80° C. This relies additionally, of course, within the reference voltage given by lC1 which includes fairly a tolerance. The temperature in which IC5 shifts status could be modified by altering the value of R9. if the thermometer is developed on the printed circuit board displayed, absolutely nothing much should go bad.

It is essential, on the other hand, that the earth of the supply for IC1, IC4 and IC5 is linked to the earth of the power amplifier. The power supply for the thermometer has to be self-contained using a transformer possessing a couple of isolated secondaries.

The sensor of this temperature meter has to be installed as near as you can to the power transistors on the heatsink. lf you would like to construct the circuit on a board of your personal style, keep the following factors in your mind. Both power supplies should be held separated from one another.

The sole a couple of connections between meter and the measuring segment tend to be plainly pointed out on the circuit diagram. lC2 and IC3 possess a distinct supply line through the output of the 5 V regulator, whilst the emitters of T1 and T2 need to have a distinct supply line through the output of lC6. IC3 will need to have its very own OV line through the regulator.

All these safety measures are essential in order to avoid lC2 being impacted by disturbance brought on by high peak currents manifesting throughout the multiplexing of the a pair of displays.

## How to Set up this Digital Temperature Meter Circuit

A precise, ideally digital, meter is needed for realignment of the thermometer.

Very first link Y and Z with each other and alter pot P4 to get a reading of 00 on the displays. After that take away the link and utilize a d.c. voltage of approximately 0.9 V to Y. Subsequently fine-tune P3 to acquire a reading of the identical value “like that in Y (calculated with the precise meter!).

Keep in your mind that the last digit is actually not shown! For example, in case the voltage at Y is 883 mV, the screen may show 88. Subsequently link Y and X with each other.

Determine the voltage throughout C5: if required, this would be tweaked to 2.73 V using pot P1. In relation to the temperature sensor, in case you’re satisfied with a precision of around 3° C, pot P2 could be disregarded.’ If you prefer a even more accurate thermometer, the sensor ought to be submerged in melting ice and P2 tweaked to provide a display of 00.

This can also be achievable to dip the sensor in water at around 37° C, and determine the temperature of the water using a clinical thermometer. P2 is actually then‘ fine-tuned to provide a display, corresponding to the reading of the scientific thermometer.