Felix2Fingerz
Active Member
Wondering if anyone has come across or used a device to control a RIMS heating element with an analog 0-10 vdc or 4-20 ma signal rather then pulsing the relay with a 3-32 vdc binary signal?
Proportional signal to SSR
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I doubt you will find that kind of controller. An SSR is inherently an on/off device. It is not possible to operate them in a linear mode.
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Triacs would do the job, but I suppose a better question is why add all that cost and complexity to something where KISS works?
A thyrister with a half wave controller work too but with less resolution than a triac.
A thyrister with a half wave controller work too but with less resolution than a triac.
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Felix2Fingerz
Active Member
There is indeed a reason for this and I would also like to explain a little more what I meant because I don't think Doug quite understood what I was looking for. Sometimes I have a hard time wording things.
I'm in the control business, building automation and been doing it for 21 years. Over the years I have accumulated many programmable controllers and all of which are very easy for me to program, wire and just plain old work with. I have one in particular that not only has all the I/O I need but also allows me to build a custom graphical interface that I can easily control via web browser. So for me, that is "KISS".
The only issue I have is the digital outputs on the controller. They will provide a 24VAC signal to a relay and all the SSR's I see want a DC voltage for the input. When it comes to programming and setting up the loops, I have always worked better with proportional outputs, analog signals and hardly ever any pulsed duty cycle type outputs.
So in the HVAC world, they have what are called SCR's. These devices were used to control electric parameter heat or air handler heating coils. The input side was analog, (0-10 VDC range). The input voltage determined the pulse rate of the output. 0 VDC on the input would be no heat and 10VDC would be full heat and anything in between would pulse the heat proportionally, just like you would want to control a RIMS heater.
So........the question is me simply wondering if anyone has come across this, maybe seen a solid state relay with a 24VAC input or what would work better for me, something with an analog input and a pulsed high voltage output. The ones I'm used to working with are huge, expensive and impractical.
Thanks. I should have worded that in more detail first time around.
I'm in the control business, building automation and been doing it for 21 years. Over the years I have accumulated many programmable controllers and all of which are very easy for me to program, wire and just plain old work with. I have one in particular that not only has all the I/O I need but also allows me to build a custom graphical interface that I can easily control via web browser. So for me, that is "KISS".
The only issue I have is the digital outputs on the controller. They will provide a 24VAC signal to a relay and all the SSR's I see want a DC voltage for the input. When it comes to programming and setting up the loops, I have always worked better with proportional outputs, analog signals and hardly ever any pulsed duty cycle type outputs.
So in the HVAC world, they have what are called SCR's. These devices were used to control electric parameter heat or air handler heating coils. The input side was analog, (0-10 VDC range). The input voltage determined the pulse rate of the output. 0 VDC on the input would be no heat and 10VDC would be full heat and anything in between would pulse the heat proportionally, just like you would want to control a RIMS heater.
So........the question is me simply wondering if anyone has come across this, maybe seen a solid state relay with a 24VAC input or what would work better for me, something with an analog input and a pulsed high voltage output. The ones I'm used to working with are huge, expensive and impractical.
Thanks. I should have worded that in more detail first time around.
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PLC/Automation/EE with emphasis in controls here.
I’ve done a number of electrically powered heating loops before it was status quo to use a digital output to control an SSR. Heating applications usually have so much thermal mass relative to the heating power input that the rapid cycling doesn’t doesn’t even show in the feedback.
The trick was to simply convert the controller output into a duty cycle. So choose a time base to work with such as 2 seconds, and if you have an output asking for 25% power then run a timer for 500ms on and another for 1500ms off.
What kind of plc are you planning to use ?
You can buy SSRs in about any coil and output voltage and current ratings you need.
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Felix2Fingerz
Active Member
In the building automation and HVAC field, PLC's are not really necessary or required like in the industrial world. The controllers I have are more commercial level which is also fine for homebrewing. I have all the same programming capabilities and I/O as PLC's, just not as precise and hearty as PLC's can be. The controller comes from the Schneider Electric product line.
After reading some of the stuff here, I believe I am going to do what you suggested and pulse one of my analog outputs into the input of the common SSR's I see.
After reading some of the stuff here, I believe I am going to do what you suggested and pulse one of my analog outputs into the input of the common SSR's I see.
Never heard of AC digital outputs. What kind of output circuit creates that?
Many SSR's are zero switching devices, meaning they will only switch on when the AC waveform is crossing zero. They switch off when the trigger signal is removed AND the output current waveform crosses zero. Thus most SSR controllers are set for time proportioning (pulse width) or pulse count modulation.
A straight TRIAC (basically back to back SCR's) can be switched on at any point in the AC waveform, and will also shut off when the trigger signal is removed AND the output current crosses zero. So, TRIAC's can be used for a form of pulse width control by varying the turn on point in the AC waveform. For full power, you turn it on at the zero crossing, and you get a full half wave of power before it shuts off. Turn it on at the peak of the AC waveform, and you get half power. Turn it on past peak, and you get less than half power. The problem is, the power percentage is not linear with the fractional trigger point in the 8.33 msec half cycle. You could linearize this in software.
If you have an analog control signal (4 - 20 mA, or 0 - 10 VDC) you have to run that into pulse width or pulse count modulator to run an SSR or TRIAC. If you have DC digital outputs, you can do the modulation in software.
Brew on
Many SSR's are zero switching devices, meaning they will only switch on when the AC waveform is crossing zero. They switch off when the trigger signal is removed AND the output current waveform crosses zero. Thus most SSR controllers are set for time proportioning (pulse width) or pulse count modulation.
A straight TRIAC (basically back to back SCR's) can be switched on at any point in the AC waveform, and will also shut off when the trigger signal is removed AND the output current crosses zero. So, TRIAC's can be used for a form of pulse width control by varying the turn on point in the AC waveform. For full power, you turn it on at the zero crossing, and you get a full half wave of power before it shuts off. Turn it on at the peak of the AC waveform, and you get half power. Turn it on past peak, and you get less than half power. The problem is, the power percentage is not linear with the fractional trigger point in the 8.33 msec half cycle. You could linearize this in software.
If you have an analog control signal (4 - 20 mA, or 0 - 10 VDC) you have to run that into pulse width or pulse count modulator to run an SSR or TRIAC. If you have DC digital outputs, you can do the modulation in software.
Brew on
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Felix2Fingerz
Active Member
The only DC outputs I have are analog, but I can configure them with a little smoke and mirrors to pulse that DC voltage on and off which is what I will have to do. Our controllers are 24VAC powered controllers so the triac outputs will output that same 24VAC. That would be one form of digital outputs they have. I also have relays with dry contacts to work with but that will require me to get a DC power supply and run that voltage through the controller relays. The on-board relays are not rated for the current needed for a RIMS heating element.
You can buy proportional SSRs. Crydom makes them, around $100 for 40A. There is another brand on eBay but I don’t recall the brand.
You may want to double check that the analog output can provide enough current to drive an SSR coil. The voltage type is high impedance.
...
Many SSR's are zero switching devices, meaning they will only switch on when the AC waveform is crossing zero. They switch off when the trigger signal is removed AND the output current waveform crosses zero. Thus most SSR controllers are set for time proportioning (pulse width) or pulse count modulation.
A straight TRIAC (basically back to back SCR's) can be switched on at any point in the AC waveform, and will also shut off when the trigger signal is removed AND the output current crosses zero. So, TRIAC's can be used for a form of pulse width control by varying the turn on point in the AC waveform. For full power, you turn it on at the zero crossing, and you get a full half wave of power before it shuts off. Turn it on at the peak of the AC waveform, and you get half power. Turn it on past peak, and you get less than half power. The problem is, the power percentage is not linear with the fractional trigger point in the 8.33 msec half cycle. You could linearize this in software.
If you have an analog control signal (4 - 20 mA, or 0 - 10 VDC) you have to run that into pulse width or pulse count modulator to run an SSR or TRIAC. If you have DC digital outputs, you can do the modulation in software.
Brew on
I looked up the Crydom proportional SSR's. Here is some info from their training module on the PMP series of proportional SSR's.
These are exactly the modes that I described in my self-quoted post. They have input circuitry that converts the analog control signal into a pulse modulated control signal, just as I described in my last paragraph.
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Yep and these are the Triac (phase angle control) and Thyrister (delivers a particular number of half wave cycles) based methods.
Triacs are good for very even power delivery, but very noisy, audibly and electrically, since they have a sharp rise. The thyrister method would likely be preferred since it turns off at zero crossings, although it has lower resolution (120 increments per second).
On a side note, SSRs that are designed to deliver AC loads are thyrister based too. But they lack the control circuits to precisely delivery a particular duty cycle.
Triacs are good for very even power delivery, but very noisy, audibly and electrically, since they have a sharp rise. The thyrister method would likely be preferred since it turns off at zero crossings, although it has lower resolution (120 increments per second).
On a side note, SSRs that are designed to deliver AC loads are thyrister based too. But they lack the control circuits to precisely delivery a particular duty cycle.
A thyristor only conducts in one direction, a TRIAC can conduct in both directions, so a thyristor can only deliver power on one polarity of the AC cycle. Full wave SSR's use TRIAC's. Both thyristors and TRIAC's can be turned on at any point in the AC half cycle (but thyristors only on the half cycles with the correct polarity), and both turn off at zero crossings in the absence of a trigger signal (thryristors shut off at the opposite polarity half cycle even if the trigger signal is still on.) Additional circuitry is used in the trigger circuit in order to get zero crossing turn on. Delivering a precise number of cycles is all done in the processing of the input signal.
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Good update Doug. I was referring to Crydom’s, MCPC series, which does not have selectable output modes (and I’m not sure which it uses, though I suspect phase angle since it needs much less logic). This PMP series looks to be newer, but fortunately it mounts using the same size heatsink screw pattern.
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Felix2Fingerz
Active Member
So I came across these for 50 bucks. https://www.gavazzionline.com/pdf/RM1EAAdatasheet.pdf A Carlo Gavazzi SSR with 4-20ma input and uses the phase angle control principle. If that will do it for me then my life got a bit easier with writing the code because in my line of work we are always controlling end devices proportionally like valve and damper actuators and VFD's. Its what I know best.
Here is the other brand I referenced above.
http://r.ebay.com/7NPsdb
http://r.ebay.com/7NPsdb
If you need a *really * big one... these are a good deal, but very big and industrial... a friend turned me on to them, great if you are electrically heating large volumes.
$2500 MSRP , 65A "WATLOW PC91-N20B-1000 POWER SERIES CONTROLLER" for cheap on eBay...
$2500 MSRP , 65A "WATLOW PC91-N20B-1000 POWER SERIES CONTROLLER" for cheap on eBay...
augiedoggy
Well-Known Member
like this?
https://www.ebay.com/itm/Douglas-Randall-SSR-Proportional-Controller-Crydom-RPC4840-Resistive-Loads-NOS/130761827918?epid=1083256454&hash=item1e7203264e:g:4N4AAMXQZdFRGZW9:sc:USPSPriority!14120!US!-1&_sacat=0&_nkw=proportional+ssr&_from=R40&rt=nc&_trksid=m570.l1313?
I bought a kyotto ssr a while with a pot knob for one of my builds which worked gret too..I always thought it was analog control like the ssrs found in these kits, No?
http://stilldragon.com/index.php/diy-small-controller.html which uses this ssr..
http://stilldragon.com/index.php/solid-state-relay.html
No, the ones I am referencing use an analog voltage or current input to drive a proportional output. These use resistance, so a standard potentiometer can be used.
augiedoggy
Well-Known Member
Thanks for explaining the difference.
Those are all standard SSVR's, which as @BrunDog said are controlled by potentiometers. They use firing phase angle control to chop up the AC waveform as described earlier in the thread.
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The $2500 controller I mentioned above that you can get on eBay for $80(I got one for $46) is truly controlled by 4-20mA and 0-10v...
Another option is a Voltage to PWM Converter Module 0-5V 0-10V to 0-100% High Quality on eBay for $4.90
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Felix2Fingerz
Active Member
Wish I waited a tad bit longer, nice price!! I did get mine in the mail and its sitting on the workbench, I need to find the time to put the pieces all together. It will be controlling the heating element to a Blichmann Rims Rocket. I just ran into my next road block. The controller I am using does not support the PT100 RTD temp sensor. I'm looking for a 2" Thermister immersion temperature probe Type I thru V.
Resurection of a dead thread. I built the calibration/verification tester for these.
