SetDimmer

[nealbert]

Help.  I am trying to vary the output of an infrared heating element and it looks like the SetDimmer function might work for that application.  I'm coming out of Output 8 of an FMD88-10, to a SSR, then to the quartz element.  I've created a Function Block with the command "SetDimmer, 4, A" where A = DM[1].  DM[1] varies form 0 to 156 and is controlled by a slider bar on my HMI.  I've tried different ladder and Function Block configurations, but cannot seem to get anything to work.  Output 8 never turns on, no matter what the value of DM[1].

The i-Trilogi Help says SetDimmer "will send a short trigger pulse to the SSR to turn it on".  So, that means, SetDimmer needs to be inside a loop??

I've searched the Forum for "SetDimmer" and found nothing. (Does nobody use this Function??) Can someone please provide some ladder and/or Function Block code that shows how SetDimmer is supposed to work?  Do I need a zero-crossing SSR for SetDimmer to work?

Many thanks,
Neal Cooper

[garysdickinson]

The FMD series PLC do not have the hardware to support the dimmer mechanism.  You will need to look at the Fx1616, Fx2424 or the Tile series PLCs if you want to use the SetDimmer hardware/software.

You can download the user manual for the Fx models from TRI’s website.  Look at chapter 18 for some info on how to wire up stuff and use the SetDimmer commands.

If you are willing to invest in a more expensive SSR you can get the dimmer functionality with the FMD PLC by using a “Proportional Control SSR”.  Crydom makes these special SSR.  You can use one of the FMD analog outputs (0..5V) to get 0 to 100% AC output when using a proportional control SSR to control your heater.
 
Best regards,

Gary D*ckinson

[nealbert]

Gary,

Thanks for the reply.  I went back to the "SetDimmer" Help screens and finally noticed the asterisk...

*{Applicable only to F-series PLC}

I'll pay more attention next time.

I've got 2 Omron proportional SSR's on order now.  I've also got a RS485 controller light dimmer that I bought a couple of months ago for a backup.  Good for 240VAC, single phase at 16 amps.  It's called a RS485 Leading Edge Dimmer and is made by Krida Electronics.  Gonna wire it up today and see how that works with my 2000 watt IR element.  Only problem is it's size.  At 3.2 x 5.1 x 2.5, it's much bigger than a SSR.  As usual my 5 lb bag already has about 9.5 lb of crap in it.  Aah, that's why they call it Development.

Thanks again,
Neal Cooper

[garysdickinson]

Neal,

Sounds like your are on a good track.  Don't let the size fool you. Most SSRs are sold without heatsinks.  If this is the case with the OMRON units, you may have to bolt the SSR to a big heat sink to ensure that it does not fry.

If your application has a big thermal mass or your application can tolerate a few degees of temperature change, you might not need much more  than on/off control of your heater.  Read "cheap SSR".

The PWM mechanism supported by PLCs is not useful for SSR as the PWM frequency is two high.  It is possible to use a pair TIMERS to build a low speed variable duty cycle system for SSRs.

Best regards,

Gary D*ckinson