Frequency Transducer.

[madhat]

They are putting in a new control system, and the bean counters cut new Frequency drives out of the contract. Three of the drives have no feed back point. Is there a Transducer I could install? Is a Sine Wave or Square wave needed?? Output Signal needs to be 4 to 20 mA Also trying to figure out the frequency range.

[kontrolphreak]

Why not just use a VFD rated current transducer and read amps?

kontrol out

[madhat]

Control company, would have to install a different program and charge us for it. That would take an RI, doubt I'd get one of them. I looked at some on the Internet, not sure how I would shield them from the line side.

[MaxBurn]

This might be misunderstood, they might not need the speed feedback (analog) but will need proof that it is running (digital). Get clarification on that, might just need a DP switch.

[madhat]

I just Emailed them back and said I no cure for the Frequency drives being cut out of the specs. The old ones are Square D and at least 15 years old. The computer shuts the AHU down if it doesn't get a feed back within so many minutes and goes into alarm.

[bacnet>CCN]

What do you mean by "the computer shuts the AHU down"? Do you mean the controller for the AHU, or is there something else in play here?
Do you have the ability to reprogram the AHU controller? It doesn't sound like you do, so I'm not sure how you'd be able to generate an analog output signal to act as an input to a controller.
Maybe an floating to analog output generator with a relay? When the fan is running a CT could close a relay that would apply 24VAC to the "increase contact" on the AUD (ACI Product), and when it's off the 24VAC would be applied to the "decrease contact". When it's increasing the analog output of the AUD would go up to whatever voltage or mA signal indicates it's running, and the opposite when it's off.

[madhat]

If the unit goes into alarm it shuts down the equipment after X number of minutes. Not sure what they are programing the time at. I can run the temperature up and down, lock controls, for an amount of time. But other than that I can't touch anything on this new system they are putting in. BTW we almost froze a building last winter, due to the pumps being programmed like this.

[orion242]

BTW we almost froze a building last winter, due to the pumps being programmed like this.

Some guys I worked with over the years swear by doing this. Argument is if the system runs out of water it could save the pumps. Seen to many times where MC may service them and fail to call anyone to reset, there they sit locked out. Freezing a building is far more a concern to me than the off chance a system runs flat and the pumps burn up. Not too often I have seen that happen. Crap freezing on the other hand...

[RezAtDorsia]

Strange that a lack on analog feedback would act like a safety and shut stuff down. I would think that would be something associated with a DI from a current clamp switch.
Seems easy enough. Whichever it is...
AI: current transducer (like Kontrol said)
DI: current sensor switch. Or the drive may have digital outputs or dry contacts (DO more likely)
Or, the response of the control system to lack of AI/DI feedback could be changed

[madhat]

I'm getting tired of writing specs, sometimes on my own time, then the bean counters say we negotiated the contract and saved money. They didn't do any bartering, just cut stuff out of the contract. The drives are over 12 years old, two are dangerous to work on, they put ABB inside Econo-flex cabinets, and kept the disconnects. This was temporary two year ago, now its permanent. Let them deal with it. BTW I found the Frequency Transducers, I'd have to put two on each drive, locate them outside the drive. Then there's the box to put them in, conduit, and whether this has to be fused.