11-14-2022 11:22 AM - edited 11-14-2022 11:26 AM
i'm begginer in NI and labsview. I try to read 4 20 ma on SCB-68a and TBX but i have some trouble. I
can measure the 4-20 ma in my Data logger and it's works very well. But when i want use NI object i can't have a good measure with same cable and resistor shunt.
I have a detector of hydrogene with 4-20 ma output to measure 0 to 5000 ppm . I use different resistor shunt 50 ohm to 200 ohm.
But when i go in NI with labsview this doesn't works properly. I'm in mode DIFF on AI/0 the 4 - 20 ma. The measure isn't stable and i have the same trouble when i use TBX or SCB with 2 different pc (6353). When i have 8 ppm in my detector i measure 3,75 ma to 4,3 ma or in my data logger i have 8 ppm after scale the data. So in NIMAX when i scale is 0 to 200 ppm.
i link Ai - to AI GND and the shunt resistor is beetwen AI + and AI -.
What i make wrong to have a good signal ? the pcie is 6353
11-14-2022 12:46 PM
To read a 4-20mA signal you need,
In the case of 6353, you're missing #2 and depending on your sensor you're missing #1 too.
11-14-2022 01:34 PM
I dont need #1 and i use already a load résistance of 50ohm +/- 0.1 ohms or 4 of this résistance.
I Have put this output in à data logger aoip and i read correcly this 4-20 ma with the résistance load beetween + and -
So i dont know what i miss you think to ohter think ?
11-15-2022 12:49 AM
I have already a source in my detector for the #1.
11-15-2022 01:16 PM
I overlooked that you already had a shunt resistor.
Please confirm if you're connecting as per the below diagram,
Please share the configuration you used in DAQmx to check the functionality.
11-16-2022 01:54 AM
I have try different too a cable beetwen 64 (AI gnd) and 37 (AI -), without.
You can see in my last photo the signal is noise, 5 mA is good because i have 200 ppm.When i have 0 ppm i'm at 4 mA with noise too.
My sensor works good because when i put this in a data logger calibrate, i have a good signal with the same resistor load and instrument cable.
I don't know what i miss because i have try all configuration in other AI and other card (TBX) it's the same.