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### Topic: pressure transducers (Read 977 times)previous topic - next topic

#### kerimil

##### Aug 14, 2011, 02:59 pm
hi, I found some failry cheap pressure transducers on ebay, the only problem is that I have no idea if I can use them with arduino

Quote
Type PA-21R/80853.3-120
Range - 0...120 bar.
Output- 4...20mA
Supply-8...28VDC.

Why the output is given in 'mA'.... is this TTL compatible?

if i supply 5V to it and attach the output to one of analog input PINs on arduino will it work ?

#### terryking228

#1
##### Aug 14, 2011, 03:13 pm
Hi, For some background:

http://en.wikipedia.org/wiki/Current_loop
http://www.bapihvac.com/content/uploads/2010/07/Understanding-4-20-mA-Current_Loops.pdf

This is an Industrial Control standard. It is fairly resistant to noise, is insensitive to length of cable, and since the current is always > 0 you can tell if there is an open or shorted cable.

You can use it by connecting the device from some voltage like 9 or 12 V DC (Greater than the 8V minimum) and to a resistor to ground.  Pick the resistor to have a voltage drop less than 5V at the maximum pressure you want to measure.

- Say that is 20mA (Max pressure). So R=E/I  so R=5/.02  = 250 ohms.  Do a little math with the Device data sheet and the 0..1023 Arduino measurement result and you have the pressure.
-- NOTE that there is a 4ma value to subtract in your math so that 4ma = 0 pressure.

Consider that the current will vary from 4 to 20 ma, and that range represents the pressure range.

4-20ma devices are usually expensive, but in surplus they can be a nice choice. Many types of sensors are made that put out this type of signal.

Let us know how you make out...

Regards,  Terry King
terry@yourduino.com
Regards, Terry King terry@yourduino.com  - Check great prices, devices and Arduino-related boards at http://YourDuino.com
HOW-TO: http://ArduinoInfo.Info

#### kerimil

#2
##### Aug 14, 2011, 03:19 pm
lol my bad, I didn't notice that the minimum supply voltage is 8V. Thx

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