Need Help

Thread Starter


Joined Apr 5, 2006
Hi Friends,

I am using a temperature transmitter connceted to my heat exchanger.
The temperature transmitter gives me current output in 4-20 ma current range.
I want to convert this 4-20 ma current signal to voltage in the 1-5 volt range.
for which i will use the circuit :

I need to convert this voltage in the range of 1 to 5 volt so that i can perform data acquisition on pc.
But i need a adc circuit which will take this input vtg and then interfacing it to the pc at the parallel port.
Plzzzzzzzzzz i need help in designing the adc circuit for the same.


Joined Apr 20, 2004

You'll find that resistors are also current-to-voltage converters. Use a small enough value so the measuring device doesn't have to develop too many volts for the 20 mills current.

A dual op amp will finish the conversion. Use the first with a pot on the non-inverting input to take the 4 mill level down to zero. The voltage will, of course, be inverted, so the second op amp will re-invert and add any necessary gain/cut to the signal level.

As for the A to D, why reinvent the wheel? There must be over 1000 different ones on the market. Or just use a microcomputer with the little bugger built in. Anything over 10 bits will do.