Hi
I have a humidity sensor that produces a linear responce from 0 to 100% RH calibrated at:
I have a PID controller that accepts 0 to 1v at the sensor input.
I am trying to produce 0v for 0% RH and 1v for 100%RH or 0.753 for
Can anyone propose a very simple circuit that will do something similar. e.g using a transistor or opamp.
Cheers
WayneL
Use an op-amp. Non Inverting input goes to ground
2 input resistors: R1 = R2 = any practical value. 1 Feedback resistor R3 = R1/(3.268-0.958) = R1/2.31 Sensor goes to inverting input through R1. Offset voltage of -0.958 goes to Inverting input through R2. . The output voltage will be negative. Invert it with an inverting op amp stage with a gain of -1. (Input R = Feedback R). . You could use any negative value of offset voltage, and then adjust R2 accordingly. For example, if you want to use -10V as the offset voltage, then R2 would = R1 * 10/.958.View in a fixed-width font such as Courier.
. . . | \\ . Vin>--[2.31*R]--+-----------|+ \\ . | | >--+--->Vout . [R] +---|- / | . | | | / | . gnd | | . +----[R]---+ . | . | . [2.31*R] . | . | . +0.958V>-----------------+ . . .
It's a DA. He wants Vout=(Vin-0.958)/(3.268-0.958)=(Vin-0.958)*(1/2.31)
Hang on Fred..... dVin/dRH is 2.31V per 75.3% change, which is 3.068V per 100%.
For preferred values. 12k/3.9k is a ratio of 3.077, or about 0.3% error.
Right- did not realize the OP was asking for both a circuit and a transfer function. To the high school dropout:
View in a fixed-width font such as Courier.
. . | . | . | . X + - - - - - - - / E . | / | . | / . | / | . | / . | / | . 3.268 +- - - - - / C . | / | | . | / . Vsensor | / | | . | / . | / | | . | / . | / | | . 0.958 + - - -A - - - - -B - -D . | | | . | | . | | | | . | | . | | | | . 0 ------+----------+-----+----- . 0 75.3 100 . . RH->
. . . . . ED CB . ABC similar to ADE => -- = -- . AD AB . . AD=100 AB=75.3 CB=3.268-0.958=2.31 . . 2.31 . Then ED= ---- x 100 = 3.068 . 75.3 . . which makes X= 3.068 + 0.958= 4.026 . . . The RH sensor puts out 4.026V at RH=100% . . . . . . DESIRED FUNCTION . . | . | . 1V+- - - - - - / . | / | . | / . | / | . PLC IN | / . | / | . | / . | / | . | / . | / | . | / . 0V+------+------------+--------- . 0.958 4.026 Vsensor . . -----+------------+--------- . 0% 100% RH . .
Thankyou very much Fred Bloggs.
WayneL
Have something to add? Share your thoughts — no account required.
Ask the community — no account required