8-channel digital display temperature controller

Here we introduce a digital display temperature controller that can test and control 8-channel temperatures. Its characteristics are that it can independently test and control
8-channel temperatures and display them digitally. The readings are intuitive, the performance is stable and reliable, and the accuracy is high. The temperature measurement range is 0-100qc
, and the 3rd digit is displayed.
    The 8-channel digital display temperature controller is shown in the figure. It is mainly composed of three parts. IC2 is a double-integrating A/D converter and
the 3rd digital display driver. It is responsible for converting analog quantities into digital signals for further processing. Finally, drive a 3.5-digit
LED (ICL7106CP drives LCD) digital tube to display the numbers. AD 590 is an IC temperature sensor. Every time the temperature
changes by 1℃, the output current of AD590 changes by 1VA, that is, AV =lpLA/C; AD590, sl-s8 (where S4~S8 are not
shown), and IC3 constitute the temperature detection, logic control and The switching circuit converts each detected temperature signal into a current
signal and then sends it to IC2 for processing. IC4 is a temperature range setting circuit to control the temperature of each channel within the set range.
The relationship between the numbers displayed by ICL7107CP (lC2) and the input analog quantities is IV=lOOO Vl/ VR EF (IV is the
displayed number, vI is the input voltage, VREF is the reference input voltage), VREF=VREF(+ )- VREF(一), in this example
VIIEF(一)=0 (@pin is grounded), so VREF(+)=VREF. In order to achieve the required accuracy and convenience of debugging,
VREF is now set to lOOmV (determined by adjusting RP2). At OoC, adjust RPi to make vl(-)=273mV (corresponding to 273K
=ooC). In this way, when the temperature rises by lqc every time, the voltage drop generated by AD 590 on Rjs after the analog switch increases AV
=lyA xlkfl=lmV, and the displayed digital change increases to IV=1000 x ImV/lOOmV=10 , because the units digit "0"
is used as the decimal point, the actual temperature rise is 1. OoC; when the temperature is loooC, R. The voltage on 5 increases to
100 x 1. O}.cA×llcfl,= 100mV, H(+) increases to 273 +100=373mV, AV=100mV, the displayed number is
loooc. IC1 is a precision reference voltage regulator that can greatly improve measurement accuracy.
    IC3 constitutes the channel selection. Every time SB is pressed, IC2 counts once, Qi to Q, and outputs high level in sequence, which
gates Sl-s8 analog conversion switches and temperature measurement probes IC5-IC12 respectively. When Qa =1, IC3 is reset immediately after VD3,
Qo =i. IC5~IC12 (Ic8 to IC12 are not shown) are 8 temperature measuring probes respectively. They convert the temperature into current through analog
switches , and turn it into voltage on Ris, and then pass through the conversion switch S (this When S should be dialed to position
"3"), add the phoenix to the K(+) terminal of IC2. IC2 performs A /
After a series of processing such as D conversion, the digital tube is driven to display the temperature value.
    The two voltage comparators of IC4 form the upper and lower temperature limit control circuits. When the temperature is higher than the set upper limit,
VD1 lights up and outputs the control signal CONi (stop heating, etc.); when the temperature is lower than the set lower limit, VD2
lights up and outputs the control signal CONz (start heating, etc.). When setting, turn S to position "2", and first adjust
RP4 to set the lower limit value. During adjustment, the voltage at A20 terminal displays the lower limit of temperature after being processed by S and IC2; similarly, adjust
RP3 to set the upper limit of temperature. After the setting is completed, turn S to position "3", and the circuit will enter the normal temperature measurement and
control state.