daq accessory card inputs and outputs

[DrKahanamoku]

So the card has 2 analog inputs and two analog outputs. The documentation indicates that the inputs are differential. Thus I take it only one sensor can be connected to the two terminals and proper bias/grounding resistors must also be used. Now for the outputs. It is unclear if there is really one or two outputs. That is if there are two outputs then is the ground terminal located near the frequency generator the ground for the two outputs or is the output actually differential. Next if the DAQ accessory is connected to an MIO 16-E4 and Measurement Automation is used, it is not clear how either the input or output should work. For my evaluation I first presumed that the input connections acted like they where expecting a ground referenced signal so I connected a wire from a frequency generator to one channel and the other end to the ground pin previously mentioned; the panel shows the appropriate sinusoidal signal (possibly twice the amplitude--need to double check that). On the other hand if I connect the frequency generator accross both input channels, one of the two wires from the generator to one channel and the other wire to the other channel, I get the following results. The panel indicates twice the amplitude signal when I look at one channel and essentially noise when I look at the other channel. I guess that this all means that the DAQ Card and panel utilize a sum signal for one panel view and a difference for the other. Is that correct? Finally when using the DAQ MIO Card and DAQ accessory for output, and utilize the test panel and a hardware scope to evalute the outputs I get the following result. When I utilize a DC output from the panel I do get that output if I wire the scope accross the appropriate channel output and the ground pin previously mentioned. Now if I utilize the frequency generator function of the panel, at any refresh? rate I get essential nothing no matter how I wire the scope. It is unclear why this is so.

I was hoping to utilize the accessory to obtain two AC inputs from an impedance head and to output a single signal to drive a power amp/shacker combination. Neither the two input, nor the AC output appears do able at this point.

[RIO-Todd]

Greetings,

The PCI-MIO-16E-4 has 16 single-ended inputs or 8 differential analog inputs. It also has two analog outputs.

When using the DAQ signal accessory you only have access to two single-ended analog input channels. While using this accessory, you don't have the option to obtain truly differential measurements from the DAQ device. This accessory was built to illustrate the different functionalities of the DAQ device in a simple manner.

If you are wanting to connect differentially to the PCI-MIO-16E-4, I would suggest to look at a connector block that will give you access to all of the 68 pins of the device. When taking differential measurements, you connect the positive terminal of your input to CH X and the negative terminal of your input to CH X+8. Therefore, to take a differential measurment on channel 0, you connect the positive terminal of the input to CH 0 and the negative terminal to CH 8. Only input channels 1 and 2 are available on the accessory and so that's why you're not able to take differential measurements with the accessory.

The ground on the accessory is connected to both the analog input ground and analog output ground of the device. When performing analog inputs with the accessory, connect the positive input terminal to Analog In 1 or 2 and the negative input terminal to the ground.

I am unable to reproduce the problems you are seeing with the accessory. I'm using the same DAQ device (MIO-16E-4) with the accessory. When I connect the sine wave of the function generator to analog inputs 1 and 2 I can see the +/- 1 V sine wave on both channels. Also, when I output a sine wave on one of the outputs, I can see that sine wave when testing it with one of the analog inputs of the device.

NOTE: The frequency of the sine wave will be slow. That might be why you're not seeing it with the scope.

I think a connector block would be more suitable for your application. I've included links to a couple connector blocks below.

CB-68LP
http://sine.ni.com/apps/we/nioc.vp?cid=1187〈=US

SCB-68
http://sine.ni.com/apps/we/nioc.vp?cid=1180〈=US

I hope this helps.

Regards,

Todd D.
NI Applications Engineer