Baldor VS drive questions

Folks,

I have been saddled with programming a Baldor VS1SP VFD. The motor is driving a peristaltic pump and I want to be able to have the pump rotate in one direction for an adjustable amount of time followed by reversing and rotating in the opposite direction for another adjustable amount of time.

I am trying to use the built in PLC functions to start a timer loop by the keypad. While the forward timer is counting up, the motor turns in the forward direction. When the forward timer reaches it limit, it starts the reverse timer. While the reverse timer is counting up, the motor runs in the reverse direction. When the reverse timer reaches its limit, it restarts the forward timer. Net result is that the pump runs constantly, while reversing its rotation every xx minutes.

I am getting all tangled up in the syntax. After I load the logical expressions based on the timer conditions, do I then load the preset speed information? Or is the preset speed information loaded from the front panel?

Thanks for any assistance offered.

Larry C

Hi Larry,

I usually start out with simple and then go as far as is justified. Your idea of a Count Up to go one direction followed by a Count Up to go the other (potentially different time) is OK.

To answer your question, the preset is the target time and the accumulated value is the time in progress. I would set up a situation where in the first timer being done (acc = pre) would one shot the second which would latch in the second and reset the first, etc. The acc on the second would begin to rack up and the acc on the first would be reset.

The timer timing (interval bits) could be used to drive the motors with one causing CW rotation and the other causing CCW rotation.

Careful attention is required to to assure that only one timer can be active at a time to avoid telling the motor to go both ways at the same time. This usually has undesirable consequences. A cross connected interlock on the outputs to insure that only one is true a time is always smart.

Depending on the type of equipment, the required methodology can very greatly but basically, the first timer being enabled would would set "Run CW" and Reset "Run CCW". When it is "Done", you would Reset "Run CW" and Set "Run CCW".

This is first grade stuff, but it sometimes takes a few tweeks due to variations in how things can look in various systems.

One word of caution, the intended operating characteristics are always fairly easy to achieve, once you dig into it. The unintended consequences are the ones that usually cause the trouble. In this case, the simple act of reversing the motor "On-the-Fly" is an example. What you may find to be much more desirable is a sequence of four steps wherein the motor can coast down before you hit it with the opposite direction. This small provision may cause the motor heating to be vastly reduced compared with the instantious reversal of direction.

So, start with two timers and build up to four, with #1 being CW and #3 being CCW and the other two set for a one to three second coast.

Have fun!

Best Regards,

Bob A.