Hydraulics Valves ON/OFF. Constant voltage or Latch Relay?

[nathand]

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@tbob wrote:
I disagree.  Digital outputs usually do not have enough current drive to actuate a relay coil.  If you use a digital out, you usually have to put in some kind of interface circuit, like a ULN2003.  But there are some digital output cards specially make for driving relays.  Digital outputs are usually 5v.  Relays can be 5v, 12v, 24v, etc.  Analog outputs typically dirve more current than digital outputs, and they are voltage configurable.

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We must work with different hardware.  As a quick example, the NI 6221 will drive 5mA through the analog output, but 24mA through a digital output.  Plus, those two analog outputs cost you an extra $100 versus a 6220, which is a lot more expensive than adding a small ice cube relay to switch the actual power to the solenoid.

[tbob]

Like I said, some digital outs are designed to drive relays.  The PXI-2567 will output 65mA I believe, and it can sink 5v or 12v.  I was speaking in general terms.  Most DIOs will not drive a relay coil directly.  Most analog outputs will.  There are always exceptions.

[RavensFan]

It all comes down to checking the specs of the DAQ device (I asked the OP for what DAQ equipment he was using, but did not get a reponse) vs. the current draw of the relay coil.

Most of the DO channels I've used were able to handle 24 VDC and the currents needed to drive an ice cube relay.

[AnalogKid2DigitalMan]

On a cautionary note-

Regardless of the analog or digital ouput used to drive inductive loads, always provide a reverse biased diode across the load to shunt the back EMF developed when power is removed in order to prevent the output from damage.

-AK2DM

[chuggins143]

Another option is to use a ready made relay board with a USB connection...  http://www.mccdaq.com/usb-data-acquisition/USB-ERB08-Series.aspx  I use the 24 relay modules with my controls and they work like a champ!  ...just my two bits.

C

[JCollado]

Do you think it would be best to use relays from NI?

I have the USB 9162 and it works well.

Thanks

[nathand]

I'm not quite sure what you're asking here.  Best for what?  What are the other options?

The 9162 is just a carrier that allows you to connect a module to a USB port, it isn't a data acquisition module.

[JCollado]

Yes I'm sorry about that. The module is 9481.

I spoke with NI Support and they say that with their Relay modules I can use digital signal and it will do exactly what I want.

I just have to send it a high signal for ON and low Signal for OFF. It will stay ON until I send a low signal. That was exactly what I wanted to know. I dint want to have an output line always sending voltage out.

With the digital signal it will make the job much simpler.

Thanks Everyone. Appreciate your help