Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.
This should control the amount of hysteresis; in other words turn on and turn off points.
The difference between the turn on and turn off points is called the hysteresis.
It should turn on at temp t1 and turn off at temp t2. The difference between t2 and t1 is the one we call span or hysteresis.
The difference should be about 1C or about 0.5C- in terms of voltage it turns about 10-5 mv.
This voltage is derived from the output of the opamp. This has no feedback and is simply working like a comparator.
This particular one cannot give 5V output if the supply voltage is 5v; we take 3.5v as the max output voltage when the turn on is in effect.
using a voltage divider, and also a small value potentiometer, you need to scale this voltage to a 0-5mv (or 0-10mv; as the case may be). The potentiometer shall provide the span control. A trimpot is ideal for this purpose because the user does need to change this regularly.
You already have this but the resistor values are wrong. A trimpot is also useful.
Let me help you to understand the basic operation.
R1 and RV1 work as a voltage divider and the voltage at the wiper should be 370mv (the set point or turn on point). Assume the input of the opamp does not take any current the voltage at the other end of R3 is also 370mv.
If the output of the temp sensor falls below 370mv, the output (of the opamp) goes high. Now some current flows through R4, R3 and RV1. This should now increase by 5mV (or 10mV; as the case may be).
If you can figure out yourself, good. Else come back as often as you like.
This should control the amount of hysteresis; in other words turn on and turn off points.
The difference between the turn on and turn off points is called the hysteresis.
It should turn on at temp t1 and turn off at temp t2. The difference between t2 and t1 is the one we call span or hysteresis.
The difference should be about 1C or about 0.5C- in terms of voltage it turns about 10-5 mv.
This voltage is derived from the output of the opamp. This has no feedback and is simply working like a comparator.
This particular one cannot give 5V output if the supply voltage is 5v; we take 3.5v as the max output voltage when the turn on is in effect.
using a voltage divider, and also a small value potentiometer, you need to scale this voltage to a 0-5mv (or 0-10mv; as the case may be). The potentiometer shall provide the span control. A trimpot is ideal for this purpose because the user does need to change this regularly.
You already have this but the resistor values are wrong. A trimpot is also useful.
Let me help you to understand the basic operation.
R1 and RV1 work as a voltage divider and the voltage at the wiper should be 370mv (the set point or turn on point). Assume the input of the opamp does not take any current the voltage at the other end of R3 is also 370mv.
If the output of the temp sensor falls below 370mv, the output (of the opamp) goes high. Now some current flows through R4, R3 and RV1. This should now increase by 5mV (or 10mV; as the case may be).
If you can figure out yourself, good. Else come back as often as you like.
LOL
the discussions are focused on hystersis for 10 days and now you find it out?:laugh:
the probelm has been fixed and the feedback network provides about 1C HYSTERSIS. (330K/1K). the thermostat is now ON and keeps the temperature bteween 37-38C accurately.moreover the relay chattering has been removed.
This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
By continuing to use this site, you are consenting to our use of cookies.
