USB6001 - DO current ratings

[MogaRaghu]

I am planning to use the USB6001 module and I notice that its digital output can only drive maximum 4mA ..

Being an industrial applications I am finding it difficult to get Relays that can interface at such low levels ( 5V / 4mA ). I know this will be suitable to drive a switching transistor base and I can have the load in the collector line. Or maybe a Mosfet .. But trying to source  relay drivers with such low current levels is a challenge.

Any ideas ? 

[GerdW]

Hi Moga,

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@MogaRaghu wrote:

Being an industrial applications I am finding it difficult to get Relays that can interface at such low levels ( 5V / 4mA ). I know this will be suitable to drive a switching transistor base and I can have the load in the collector line. Or maybe a Mosfet .. But trying to source  relay drivers with such low current levels is a challenge.

Any ideas ? 

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Use a MOSFET or a switching transistor…

(You might even include optocouplers to provide galvanic insulation.)

[rolfk]

Your first and foremost problem is the use of "USB-6001" and "industrial application" in the same post! 😀

While I already hesitate to use USB in general in industrial applications, but sometimes it is unavoidable, doing so with a cheap low cost device is definitely going to be painful in the long run. One of the reasons it is cheap is because it uses standard CMOS circuitry directly connected to the IO ports. That is cheap of course but also unsafe.

Aside from the small possible current, a CMOS output will inevitably be destroyed by the inductive reverse voltage when you switch off the relay. Even a flywheel diode across the relay will not protect the CMOS output for infinite time since depending on the wiring and/or PCB layout, there will be transients that surpass the power supply voltage for the CMOS output and cause leakage currents through the internal parasitair junction diodes of the CMOS circuit that will over time damage the circuit anyhow. Not a problem for your typical home automation project using an Arduino or Raspberry Pi board but definitely not something to use in an industrial application.

[crossrulz]

Based on your signature stating "LabVIEW to Automate Hydraulic Test rigs", you really should be using a cRIO.  Using the FPGA backplane, you can enable safety requirements no possible with a simple USB device.  And there are plenty of C-series modules that are specifically made for industrial situations.  It will cost a lot more, but that is what is required if you want to protect your test system, the UUT, and most importantly people.