AC Motor starter contact circuit

[Mr_Papagorgio]

What is the best method for controlling an AC motor starter contactor with labview? The motor is 480VAC and the coil is 24vdc, attached is the wiring diagram when using push buttons as well as a ladder logic diagram. I've done both the push button and ladder logic methods, but am at a loss when it comes to using labview. Any ideas?

[GerdW]

Hi Mr,

I'm not familiar with ladder diagrams, but with eletric schematics…

What about a simple

MotorON := StartButton AND NOT(StopButton)

boolean logic computation?

All you need in LabVIEW are two buttons on the frontpanel…

[RavensFan]

Is this really a LabVIEW question, or more of hardware question?  For LabVIEW to control it, you'll need a DAQ device that either has relays, or a digital output with a 24V rating and enough current to drive the coil of the contactor.

[Mr_Papagorgio]

GerdW,

That would work, but the primary benefit of the push button and ladder logic circuits is if the motor looses 480VAC due to a breaker or overload tripping, the motor will not automatically turn back on once the breaker or overload is reset. If the VI uses just a simple pushbutton and the motor looses 480vac, once 1480 vac is restored the motor will come back on.

Ravensfan,

You could achieve this with wiring / hardware, but it would be nice to do it programmatically like the ladder logic diagram does.

[RavensFan]

You need to have SOME wiring and hardware on order for a piece of software to control a motor contactor.  The relay logic can be replaced by code in software.

But your question wasn't clear about where you were stuck.

If you really want to make sure the contactor disengages on an overload condition, you should it wire up like you show in either of your diagrams.  Use latching LabVIEW buttons that will temporarily energize the start and stop relays so your software controlled physical relays will behave just like the hardware buttons in the diagrams.  And with anything software controlled, I'd recommend having another physical hardware E-stop button so you can stop the motor even your software crashes for some reason.

(Tip:  "Loses" not "looses")