I was wondering if there is anyone use ProSense pressure transmitter I have 3 PTD25-20-0200H and I'll like to make an Autoclave using them, and i was wondering if anyone can help me to find out if this sensor can be use with an Arduino Mega to read the pressure.
the folowing are the links for information and Datasheet.
Thank you
Yes, if you run the 4 - 20 mA output current through a 250 Ohm resistor you will get 1 - 5 volts which you can read with the Mega's analog to digital converter and get a reading from 204 - 1023. 0 pressure = 204, 200 PSI = 1023. Or pressure = (ADC reading - 204) / 818 * 200. You should put a current limit resistor in series with the analog input pin, value depending on the sensor's supply voltage (Vsupply / 0.0009) or a 5.1V Zener diode between input pin and GND.
EDIT: You can get close to 250 Ohms by putting a 3300 Ohm in parallel with a 270 (both are standard values).
thank you for your great input, now i need to try it and let you know, i just order the Zener Diods can't wait to test it... thank you again!!!
250ohm means you're going to use default Aref, and rely on the stability of the Mega's 5volt rail.
Bad idea.
The Mega has in internal 2.56volt Aref (called in code), which is potentially much better.
That means the sense resistor should be ~125ohm.
That also would eleminate the need for a 5.1volt zener, which is also a bad idea (temp dependent non-linearity).
Wise to use a 10k resistor between sense resistor and Arduino pin (safety), and a 100n cap from Arduino pin to ground.
Let us know if you need a diagram.
Leo..
Wawa:
Wise to use a 10k resistor between sense resistor and Arduino pin (safety), and a 100n cap from Arduino pin to ground.
Let us know if you need a diagram.
Leo..
if you have a diagram that will be great!! thank you
Theoretically, the sense resistor should be 2.56 / 0.02Amp = 128ohm for a Mega with 2.56volt Aref enabled.
Best to choose the value slightly lower. 100ohm+27ohm in series would do.
For an Uno (has only 1.1volt Aref), you could use a 51ohm resistor (E24 value).
That would also work for the Mega, if 1.1volt Aref is selected.
How to use Aref can be found in the Help>Reference>analogReference part of the IDE.
Leo..
Wawa:
250ohm means you're going to use default Aref, and rely on the stability of the Mega's 5volt rail.
Bad idea.The Mega has in internal 2.56volt Aref (called in code), which is potentially much better.
That means the sense resistor should be ~125ohm.
That also would eleminate the need for a 5.1volt zener, which is also a bad idea (temp dependent non-linearity).Wise to use a 10k resistor between sense resistor and Arduino pin (safety), and a 100n cap from Arduino pin to ground.
Let us know if you need a diagram.
Leo..
I def. would if you could....
Thanks
outsider:
Yes, if you run the 4 - 20 mA output current through a 250 Ohm resistor you will get 1 - 5 volts which you can read with the Mega's analog to digital converter and get a reading from 204 - 1023. 0 pressure = 204, 200 PSI = 1023. Or pressure = (ADC reading - 204) / 818 * 200. You should put a current limit resistor in series with the analog input pin, value depending on the sensor's supply voltage (Vsupply / 0.0009) or a 5.1V Zener diode between input pin and GND.
EDIT: You can get close to 250 Ohms by putting a 3300 Ohm in parallel with a 270 (both are standard values).
Thanks for the reply, very actual for me now!
@Wawa:
Why is a Zener not good? I've only used them in PS type circuits. 
outsider:
@Wawa:
Why is a Zener not good? I've only used them in PS type circuits.
Zeners are not ideal. They don't have a sharp zener voltage "knee-point".
They already start conducting below the zener voltage, and anything that is not ~5.6volt is temp dependent.
That could make the ~20mA top area of the 4-20mA sensor non-linear.
When you use a lower value sense resistor, e.g. ~51ohm with 1.1volt Aref or ~128ohm with 2.56volt Aref (Mega), and 10k current limiting for the internal pin clamping, then over-voltage protection becomes less of a problem.
You can safely use the 5.1volt zener with a lower value sense resistor, because sensor voltage at 20mA will stay well below the knee-point of the zener.
I should have added a diode across the sensor, to protect against negative voltages.
But a zener across the sense resistor will also take care of that.
Leo..
@Wawa:
Makes sense, TNX & K++.
how will I make the loop? I'm trying to sketche it in Fritzing but I don't have the sensor so I used a Solenoid, but I don't understand the loop.. if I use 12 Volts for powering the Valve... Thank you
Are you using the diagram from post#5, with a 51ohm sense resistor?
Then you can use a 12volt regulated supply for the sensor, and share supply ground (-) with Arduino ground.
12volt supply (+) to sensor (+), pin1.
Sensor (-) pin2 to the 51ohm resistor (current loop (+) in the diagram from post#5).
Post a diagram, so we can check if you understand it.
Leo..
I was wondering if this looks ok? I used the Solenoid sensor to represent the PTD25-20-0200H sensor...
were you able to download the image i attached to
Wawa:
Are you using the diagram from post#5, with a 51ohm sense resistor?
Then you can use a 12volt regulated supply for the sensor, and share supply ground (-) with Arduino ground.12volt supply (+) to sensor (+), pin1.
Sensor (-) pin2 to the 51ohm resistor (current loop (+) in the diagram from post#5).Post a diagram, so we can check if you understand it.
Leo..
were you able to download the image i attached to see if I did it right ...
That's not how I explained it in post#12.
Leo..
here is what i had before, and i got confused by #5 post... I used a 220ohm resistor to use 24V because I have to use 2x 24V Solenoid Valves... and 7 thermocouples...
I hope that this is right now!! thank you so much for your patients and help!!!
That's electrically correct, but without the extra 10k/100n protection.
220ohm sense resistors also assumes you're going to use (the potentially less stable) default Aref.
Not sure why you think that 24volt has anything to do with it.
Leo..
I'm just worry about burning the Arduino mega with 24V... I added the 10k resistor and the 100nf Capacitor, I hope that's correct now...
That part is ok now.
Time to learn about the Mega's internal 2.56volt Aref.
Replacing the 220ohm resistor with a 120ohm resistor, and calling the 2.56volt Aref in setup(), will give a more stable readout from the 4-20mA sensors than default (5volt) Aref.
Leo..
