Discussion in "ARM Development" started by    diana1234    Mar 20, 2015.
Fri Mar 20 2015, 12:34 pm
#1
Hi,

Please guide me, how i can interface a 4-20mA pressure transducer with my microcontroller(LPC2478-ARM7),
how i can read its output current, so that i can display the present pressure over a display.
Thank you
Sat Mar 21 2015, 04:28 am
#2
The simplest way is to pass the 4-20mA through a 150 ohm resistor,
to create a voltage between 0.6 and 3.0 volts.

Use the ADC built into the LPC2478 to read the voltage as a 10bit value.
 ajay_bhargavdiana1234 like this.
Mon Mar 23 2015, 11:54 am
#3
Thank you ExperimenterUK for the reply,
Should i direct place 150 ohm resistor between Transducer signal wire and ADC channel or there would be any other biasing circuitary?
Please elaborate with some example circuitary to do this.
Thanks in advance.
Mon Mar 23 2015, 03:00 pm
#4
You need to connect resistor in shunt to measure voltage across it.
 diana1234 like this.
Tue Mar 24 2015, 10:44 am
#5
There would be no any biasing circuit?
only a shunt resistor will do the work
Tue Mar 24 2015, 11:02 pm
#6


There would be no any biasing circuit?
only a shunt resistor will do the work

diana1234


Just connect the sense resistor between the transducer output and ground.
Add a small (say 1 uF) capacitor in parallel with the resistor
to give a bit of smoothing.
You can calibrate in software or by adding a variable resistor.

If the sense resistor becomes disconnected you will get a high voltage
at the transducer output, make sure your connections are good !
This circuit has smoothing, voltage protection and is adjustable.

 diana1234 like this.
Wed Mar 25 2015, 11:04 am
#7
Thank you sir
I make a try with the transducer and let you know.

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