# 4-20mA to usb/serial

Discussion in 'General Electronics Discussion' started by liambrett, Sep 4, 2009.

1. ### liambrett

3
0
Sep 4, 2009
Does anyone know of a device and accompanying s/w which takes in a 2-wire 4-20mA signal then connects to computer via serial or usb, and a piece of software which will display the value scaled over a given range?

2. ### tron-ee

12
0
Sep 11, 2009
Hello liambrett,

See:
www . dataq . com /products/startkit/di148.htm (remove the spaces)

This gadget is an analog to digital converter, \$50, (with drivers), is powered by the USB data bus. Shunt one of the analog inputs with a resistor and then you stick the resultant data stream into an Excel spreadsheet for readout, where you can scale the data into the range you desire. 4 - 20 ma

Remember, Ohm's Law = E over I x R....

E
======
I | R

Make the above on a peice of paper, stick your finger over the letter-function you
need to know. Above the line you divide the bottom into the top, below the line, you multiply I x R = E, stick your finger over R, you divide E / I = R, etc.

E = Potential in Volts
I = Current in Amperes (or mA...4 mA = 0.004 Amp)
R = Resistance in Ohms

So, lets say you shunt an input with a 100 Ohm resistor,

4 mA x 100 = 0.4 Vdc
20 mA x 100 = 2.0 Vdc

This should do it for you.

tron