Multifunction DAQ

Are you talking about the PCI-6025E? The various ports on the 6025E are controlled by different chips and do indeed have different current sourcing capability. The DIO 0-7 lines are controlled by the DAQ-STC chip and can source about 13mA and can sink even more. The PA, PB, and PC lines are controlled by a separate 82C55A chip which can only source or sink 2.5mA. Please see pages 3-1 and A-7 in the 6025E User Manual for more information.

If you need higher current capability on more than 8 lines, you could use the ER-8/16  relay modules. Please see Figure 3-3 on page 3-9 of the
ER-8/16 User Manual for details on connecting the relay modules to your DAQ board. This manual was published before the 6025E released, however the compatibility is the same as the AT-MIO-16DE-10. Configurations A, B, and C are valid for your board and will give you an additional 8, 16, or 24 lines respectively.

Regards,

Brent R.
Applications Engineer
National Instruments

Yes, I did mean the PCI-6025E (long day). I understand what you are saying about the lower current output from the 82C55A chip, but I would really like to avoid an external relay module. The valves I am powering through the PCI-6025E are mounted on a circuit board that already has an integrated SPDT relay for each valve. These relays have three positions: manual (on), center off, and auto. From what the manufacturer is telling me, if the switches are in the "auto" position, I need to put -5VDC across that relay to turn on the valve. Up to this point I had been wiring the valves directly to the I/O screw terminals, but I would like to use the circuit board's wiring (with the switches in the auto position) to connect the valves.

So my new question is:
Will I be able to output -5VDC with the PCI-6025E with either the DIO 0-7 or PA, PB, PC ports? If I need a new DAQ card or relay module (preferably one card instead of 2 devices), what is the best solution for output of -5V, with adequate current output?

Thanks again for your help,
Brian

Well, first it is important to find out how much current the relays will take. The lines on the DIO port of the 6025E can source/sink up to 24 mA. So if you can find the impedance of your relays, you should be able to calculate whether or not you are exceeding the current limitations of your DIO.

Now, perhaps a better device for your application would be the 6527 Isolated DIO board. The solid-state relays on this board can handle up to 250 mA! Otherwise, you will need an external module such as the ER-8/16 or the SC-2061. In either case, you will have to look at the User Manuals to make sure they can handle the amount of current you require.

Hope this helps!

Russell
Applications Engineer
National Instruments
http://www.ni.com/support

How much is "adequate" current output? If the DIO lines on the 6025E were working fine, then adequate seems to be 10mA or so. The 6527 would be perfect for up to 24 channels. It will switch 120 mA, which sounds like it should be plenty. The 6533 is overkill in terms of speed (20 MHz), but it'll provide 24mA and would be good for up to 32 channels.

If you can make do with 24 channels, the 6527 is ideal. It's very inexpensive and it works with the 100 pin cable you probably already have.

Regards,
Brent

Oops, Brent is right. The 6527 does 120 mA, not 250 mA.

Thanks for the advice, guys. The valves I have operate at 5V and draw 0.65W of power. Assuming that 10mA is enough source/sink for this application and that I'm not having some other issues (my electronics background is really limited!), the 6527 looks like a good solution. Do you think I would run into any problems if I were to use the 6527 to control 12 12VDC valves (power=0.65W)?

Thanks again,
Brian

Yes, the 6527 should be ideal for your application. You'll also need an external 12V power supply in order to provide the drive current for the valves. This is pretty much unavoidable, afterall a computer's power supply can only do so much. (The outputs on the 6527 are actually solid-state relays.) The 6527 User Manual should tell you every thing you need to make your connections properly.

Best Regards,

Russell
Applications Engineer
National Instruments
http://www.ni.com/support

Okay, I'm a little confused. I have attached below a diagram of the system as I understand it. The 6527 acts more like a switch than a source or sink. The power requirement of the valves does not matter as long as the relays can handle the current, which they should if they were put on the PCB specifically for this purpose. As long as the input current to the relay is less than 120mA (it probably is much less) then this will work fine. If the input current to each valve is less than 120mA then you could skip the relays altogether.

Regards,
Brent

Sorry to confuse things with the different voltages! Here's a summary of what I have (see attached doc). I have a PCB with valves, manifold and switches all integrated. The board originally came with 12V valves (0.65W), but I want to control this thing with digital I/O ports via LabVIEW, so I swapped out all the valves for 5V (0.65W) valves. They are wired into the white surface mount power connectors, and the board is powered with 5V (upper left on first picture). I can control the valves manually by flipping each switch to "on". With the switch in "auto" and the wires from the 25-pin connector connected to the I/O block, I have a VI that uses a digital port write to control the valves.

This works absolutely fine for
DIO on the PCI-6025E, but the valves simply won't open when I change the wiring and run the same program using PA, PB or PC. From what you have said, I assume this is because there isn't enough current coming out of the 82C55A chip. I really want to use the built-in relays on my PCB since this means I can use the 25-pin connector to interface with the NI card, so the external relay module isn't a good option.

If you think the 6527 will do the job I need (exactly what DIO of the 6025E does!) then I'll go with that one. From looking at the current specs for the 6025E(13 mA ouput at 5V), I can't say I understand exactly why this one port works, but it does.

You guys are great for getting back to my questions so quickly.