Help wanted with loadcell to daq wiring and grounding

[eichlerjw]

Hi

I am acquiring data from a load cell using a NI-USB-6211 OEM board.  Under certain conditions I am seeing large spikes in the data which I think are caused by noise.  The DAQ card also outputs a 0 -10V analog signal to an AC actuator controller to control its output. The current setup is:

Analog input: Novatech load cell wired to a Novatech 'SGA' (strain gauge amplifier).  A 0-10V output from this amplifier is wired to the AI 0 and AI GND terminals on the card.  I am using the RSE configuration.

Link to SGA manual [url]http://www.novatechloadcells.co.uk/pdf/sgamanual.pdf[/url]

Analog output. Wires connected to the AO 0 and AO GND terminals. RSE terminal configuration.

I have attached a schematic diagram of the setup

I understand that the AO GND and AI GND terminals are linked.  My concern is that some noise is being created by the AC motor controller and this is interfering with the measurements from the load cell. Is this possible and can anyone suggest a better configuration to avoid this situation if so? I'm thinking that at some point one of my negative wires should be grounded but I'm not sure which one.

Many thanks.

John

[eichlerjw]

I forgot to mention that the strain gauge amplifier is mains AC powered but does not have an earth connection. The mains cable only has live and neutral cores.

[RavensFan]

I would take a look at the analog input wires from the load cell amplifier and also the analog output wires to the motor controller with an O-scope to see if you see the noise on either one of them.  Also, look at the main power supply lines if your O-scope can handle those voltages.

Your strain gage amplifier probably doesn't need a ground on its power cable otherwise it would already have one.  It is probably designed in a way that there is no need to worry about a dangerous electrical short.  And the instrumentation side of the amplifier is probably a floating voltage reference.

You may want to consider and optoisolator on the analog output lines to the controller (in case the noise is coming through that way), or a line filter on the AC lines going into the motor controller.

[eichlerjw · Accepted solution]

OK - thanks for the quick reply. Tomorrow I will try to acquire data from the load cell using the DIFF configuration. Maybe this will help to reduce the noise.

cheers

John

[eichlerjw]

Update: changed the wiring from NRSE to differential and all the spikes disappeared!

thanks for the help

cheers

J

[s_t]

i am working same thing i want acquire signal form Load cell for Different Weight ,

I am making weighing application ,can u help me or share th vi to acquire the Signal.

Thank

shishir tiwari

[eichlerjw]

Hi. Please see the attached vi. This is an example of how to read the signal from a load cell. I suggest you read up on DAQMX data acquisition. The help files and examples that ship with labVIEW are very useful. Go to help>find examples and search.

I hope this helps.

Cheers.

John