Getting only half wave during data acqusition

[ndLabVIEW]

Hello all,

              When I acquire data using cDAQ NI 9215 and chassis 9171, my data is getting tripped/hatched by the lower side ( I have attached a file for your reference). And this happens with some channels at different times while other channels give good output. Kindly, help with the problem with this. What can be done to rectify this problem?

Figure 1: tripped/hatched signal

Figure 2: tripped/hatched signal

Figure 3: Estimated result.

Note: I also checked with NI MAX Test Panel, I am getting similar results.

[crossrulz]

Are these signals floating?  Or the grounds are not referenced to each other?  That is what this looks like.

You might want to have a look at this article: Field Wiring and Noise Considerations for Analog Signals 

[Henrik_Volkers]

Most likely (IMHO) a missing Input Bias current path.   Solutions in the link crossrulz provided...   (one or two 1Meg resistors from the anlag - input (or both)  to AGND usually solve that.  

[RTSLVU]

I have noticed similar results when the vertical range is not correct.

[ndLabVIEW]

I am using NI 9215 and Current Transformer sensor connected vai BNC cable.

[ndLabVIEW]

Can you tell me how to correct this?

[crossrulz]

Your sensor is likely floating.  This means it needs something to pull it towards ground.  Added 1MOhm resistors on each side of your transformer to AIGND should do it.

[ndLabVIEW]

Thankyou for your answer. Can you guide me how to ground this using resistor. I am using current transformer and a BNC cable for this.

[Henrik_Volkers]

Which type of 9215 do you have? The BNC input version should have a 100kOhm Resistor to AGND/COM already ... 

Which version are you using?

For the screw or spring version try a 1M Ohm resistor between AI- and COM terminal 

If you use the 9215 BNC version and you run into that problem, please provide  a schematic of all your cabling. Do you have a handheld multimeter  (DMM)  around? can you check the voltages at the BNC shield .. between the shields and to PE/Ground ?

I don't have a 9215 (BNC) around, but I assume you should measue a resistance of 200kOhm with the DMM from one BNC connector shield to the next channel BNC connector shield. (Just in case one 100k is blown in history)

[ndLabVIEW]

I am using 9215 (BNC).