Issue in Analog input in PIC16F877

Thread Starter

ecaits

Joined Jan 6, 2014
56
Dear Friends,

I am working on PIC16F877 with hi-tech c compiler.
I have used 0-5V analog input but in field, I am getting 4-20mA output.

Can I use 4-20mA as analog input or I need to convert 4-20mA to equivalent 0-5V??? How can I use it???

Plz suggest me.

Nirav
 

ericgibbs

Joined Jan 29, 2010
18,740
hi.
You could use a 250R resistor to terminate the current loop.
For 20mA you will get a voltage of 5V across the 250R.
At 4mA a voltage of 1V, which you could subtract within the program.

Giving a span of 4Volts
E
 

paulfjujo

Joined Mar 6, 2014
23
hello,

You just have to check:
- if you can connect the Cold point of 4-20mA signal to your 0V PIC power supply, together.
without galvanic insulation problem..
- if you don't allready have other device in this 4-20mA loop
- if your 4-20mA loop is an Active loop (deliver the current , so not a passive loop)
- in case of 250R brocken, you can get all Voltage of the loop (12V or 24V!)
on ADC input..
 
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