Negative Analog Output from PCI-6229

[Jameshobiecat]

I appreciate this question may sound a little elementary to some of you but I have spent hours searching for an answer with no luck.

I have a NI PCI-6229 M series I/O card that I want to use to control a hydraulic proportional valve. The valve in question takes inputs in the range of -10v to +10v which happily is the output range of the I/O card.

My question is this; in order to generate a negative (-) voltage across the valve, do I need to connect to two AO terminals (i.e. AO0 and AO1) or can I connect to a single AO terminal (AO0) and a ground (AGND)? Or to put it another way, can the hardware generate a voltage lower than ground thus creating a negative potential difference across the valve if an AGND is used?

Many thanks.

James  

[Dennis_Knutson]

The output voltage spec is referenced to gnd and this is for a single channel like AO0.

[Tori.M]

Hi Jameshobiecat,

How are you trying to code your output generation?

If you're wanting both the negative and the positive outputs from the card into your pump use say AO0 for negative, and AO1 for the positive, then generate with coding as shown below:

This coding would be for the negative output i.e. -10V.

In order to ground your signal you would need to connect the Gnd of your pump to the Gnd of your PCI card.

Hope this helps!

[Jameshobiecat]

Hi Tori,

I am using the xPC Target toolbox in MatLab to generate the controller code so am not directly coding it as such.

I have connected the GND terminal of the valve to the AOGND terminal and the signal terminal of the valve to AO0. May aim is to be able to generate a full range of control signals from -10v to +10v whilst using only one of the four analog output channels on the 6229.  

Am I going about this in the correct way?

Many Thanks, James

[Tori.M · Accepted solution]

Hi James,

My mistake as I'd assumed that you were using LabVIEW. In theory, you should still be able to set the output programmatically.

This link from the MathWorks website shows how to vary the values of your Analog Output when someone was using a PCI device so may be of some help.

I reckon that the National Instruments Analog Output block is likely to also be of some help.

Having not used the xPC Target before, it's hard to be sure though. I'd definitely recommend using LabVIEW next time

And yes I do reckon you've gone about your wiring the correct way.

Kind regards,

[Jameshobiecat]

Tori,

I am confident that everything is fine from a software point of view; xPC does make setting up the outputs near fool-proof.

It was the ability of the 6229 to generate a voltage lower than that of the ground, and thus it’s ability to send a negative signal to the valve if a single AO channel and an AOGND were used, that I was slightly unsure of. Thank you for confirming this.  

Regards,

James