VFD to control heaters ??

Honestly, if you really want to use an ultra-cheap, 0-10VDC input, proportional output control, use a simple fractional horsepower Minirik DC Drive. You can probably find a cheap DC drive that can run directly off of 120VAC, deliver 0 to 90VDC at 5 or 10 amps that costs under $75.

It's also much safer for a classroom enviornment, as there are no bus-caps that remain charged after the power is disconnected.

Try a Thermistor

Dan,

I did the same thing in college. Controlled temperature via a PLC and a SSR. Try using a Thermistor to measure the temperature, it worked quite nicely for me and was cheap. I did however have to do a little interfacing circut to bring it into the plc's analog input. In my case as well, I didnt use a relay output from the PLC to drive a SSR, I drive an external PWM circut via a 0-10Vdc output from the PLC. Had to make it more interesting somehow..

Just my $0.02

Andrew Evenson

I think Dan's point is that when you enroll in a course, you usually don't prepare for or expect to have to also buy the equipment used in the course, even if it is relatively cheap! How many of you have bought equipment to use in school? A lot of schools now would not allow students (if they knew about it) to purchase or contribute equipment anyway due to the legal liability issues. He hasn't mentioned that his school has a DC motor available for experimentation. What he has said is some AC VFDs, old DC drives, a PLC, and thermocouples.

LANCIE

I touched on it - BUT
School does have several DC drives just sitting. With budget and all that stuff, it makes sense to use what you got. Also instructor wants more setups where PLC is "main controller", so a PLC controlling a DC drive to provide varying level of heat would be perfect.

In an effort to atone for my sins of "pack rat itis" I donated a 1 HP 3 phase B & G pump. Reason was instructor wants to setup a test stand / demo for PLC control - in this case use it for controlling a tank level. I addded a heater to allow for another PLC application.

Pump was gathering dust for 10 years, I am now in a state of grace I be saved I dun see the lite.


Hmmm light lessee now - we got the pump for irrigation, we got heat so if we setup / simulate a greenhouse then all we need to do is control both the light level and a specific waveband of lite (blue I think) to get optimal plant growth. Now all we need is a source of CO2 for the plants to feed on.
Here I go again getttin all complicated.

Thanks for help
Dan

Could you use just one heater for the analog control and the rest contactor driven? By this I mean having a relatively small control, trim (whatever you'd call it) heater . The other heaters would be course or "major heaters" that would come on or turn off as the control heater reaches its control limits (E.g. SCR control
SCR controller < 30% or > 90%). I do this very often with tank heaters.
I tried with my furnace though and blew my house up. So, be careful and keep a rabbits foot with you at all times!

Is 9 years old the record for a PLCS.net reply?

temperature not to hot maybe need adjustment the temperature

Sorry about that wise guy. The post showed up in a search and w/o my specs on my optical sensors, the year looked like 14 not 04. NEway the only thing I lost was just a few skin cells on my finger tips. If it puts a kink into the continuity of this board....you should flag it. On the other hand, perhaps someone has the question right now and I've preemptively aswered it.

HJTRBO said:

Is 9 years old the record for a PLCS.net reply?

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I doubt that this is a record, since it does happen sometimes.

lee1968nh said:

Sorry about that wise guy. The post showed up in a search and w/o my specs on my optical sensors, the year looked like 14 not 04. NEway the only thing I lost was just a few skin cells on my finger tips. If it puts a kink into the continuity of this board....you should flag it.

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Excuses, excuses... Just kidding. I actually enjoyed reading this old thread. I don't think anyone will be upset by one more zombie thread. It is no big deal.

Paul

I don't think anyone will be upset by one more zombie thread. It is no big deal.

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Right, no records for the oldest revived post. However there might be a record here for "first house blown up"!

I tried with my furnace though and blew my house up.

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