Love controller wiring question

So I picked up a pair of these Love 4B-53 1/4 DIN modules (pre-owned but NIB). Now I am looking to wire them up in heating/cooling ferm chambers and see that they are technically listed as (1) current output and (1) relay output as opposed to 2 current outputs.

Am I right in interpreting this as indirectly stating I need an SSR for one of the 2 outputs or does it imply that I can only use one output "at a time" as current output?

Here is the wiring diagram from Dwyer's site:

I had a Love 4B controller, but returned it because the ramp/soak mode did not work like I expected. It would only do ramp/soak in conjunction with PID control. I wanted it to do On/Off control with ramp/soak. This is because I was using it to control a compressor-based freezer, where PID control is not appropriate. In the process I learned alot about these controllers. So back to your question. The end code (e.g. 53 in your case) indicates how each control channel is hard configured at the factory. In your case, one output is current control and the other is relay and this is fixed. Of course how/if you can use these totally depends on your equipment. E.g. a compressor based freezer pretty much would need to have a relay in On-Off mode. I'm not too familiar with equipment that uses current control, but I would guess that you could find some heating device that could use current control.

I would also add that I think current control is normally used in PID mode where the output is a continuous variable (amount of current). So current control is not for hysteresis On/Off control.

Hex23 said:

I would also add that I think current control is normally used in PID mode where the output is a continuous variable (amount of current). So current control is not for hysteresis On/Off control.

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Ok, not really sure I understand that statement. I thought the current control could be used for a resistive load (like a light bulb or a resistance based heating mat, for example) and it would still be totally fine for heating/cooling mode with hysteresis. Is that not how you understand it?

Let me first state that I have been pretty disappointed with the lack of detail in the manuals for these kinds of devices. For instance you'll find nowhere that explicitely states that a relay can be used in PID mode and that the way that is achieved is by pulse width modulation. I think some of this is due to what the authors think is common sense and also due to general knowledge and concensus that has built up in industrial controls.

So, I am really just guessing based on the limited amount of information in the manual about current output (4-20 mA). Sounds like it would be something used for PID continuous variable output.

I apologize if you already know this but ...

Hysetersis is a term most commonly applied to simple On/Off control (think home thermostat). The output is either On or Off depending on the relationship to the measured variable, set point and hysteresis value. Hysteresis is mainly to prevent fast cycling.

PID is Proportional/Integral/Derivative control where the output is a continuous variable (not binary On/Off). It could be in the form of a voltage or current level or even PWM of a binary signal. The level of the output is based on the difference between the set point and measured value (AKA error). The error is multiplied by a proportional term. The difference in error from cycle to cycle (derivative) is multiplied by a derivative term. And the historical accumulation of error (integral) is multipled by an integral term. These values are added together to get an output. Controllers implement some combination of these to achieve the desired control properties (responsiveness vs overshoot, etc). E.g. you could have just P+I. PID control is generally better than On/Off, but can't be used on some equipment because the equipment does not take a continuous variable output. E.g. a compressor in a standard freezer is either on or off. You aren't controlling the speed of the compressor. Some things like a resistive heating device could probably do either with the right circuitry.

If you have equipment that can be controlled through current control in the range of 4-20 mA, then I would guess that it would work. It would have to be something where the current is transformed/amplified into a larger signal. e.g. 20 mA is not capable fo generating heat in a standard lightbulb - you'd have to have additional circuitry. I'm not very familiar with heating equipment. That's my next project for my fermentation chamber.

Yep, understand the hysteresis and PID concepts, just trying to apply it to a wiring diagram and iffy-at-best documentation. I would hate to wire something up and fry the controller.

I was thinking ON/OFF control anyways. I will be using this for Sanke-fermenter-filled control and the thermal mass of the kegs will allow quite a bit of "slow moving" action to the thermal control aspect, at least I predict so. That being said, I don't think ambient air cooling with a small freezer component or small ehating mat is really going to go off the handle and be over-shooting by several degrees. I think in this regard it's all about how I set up the hysteresis points for ON/OFF control of the 2 elements.

That being said, I sent an e-mail to Tech support at Dwyer, although I have read that they are typically not very helpful. I figured if I framed it as "which SSR's do I need to buy and can you confirm the wiring diagram for my 4B-53" it would get a response since I will be buying some kit to go along with the question.

Given my experience with the B series controllers and their inabililty to mix certain control modes and output, the question I would ask is whether you can really do On-Off control with the current control output. If the current contol mode is built for linear output PID, I'm not sure you could successfully use it for On/Off control. Or put another way I don't know whether the current control is normally used to control an SSR. I found a manual to an appparent predecessor to this contoller (see http://www.mod-tronic.com/mod_pdf/love_pdf/1600_manual.pdf). It seems to be calling the current output mode "proportional current output", which leads me to beleive this is for PID mode.

I suppose if you had equipment that itself turned on at a given current threshold and off at another (perhaps with some hysteresis) it could work, but I'm not familiar with such equipment. I suppose you could even design a circuit to do this. Maybe an SSR could even do this for you.

Yes, my experience with Dwyer support was less than stellar. Their first line support seem more like salesman than engineers. I ended up buying a similar controller from Auber instruments. While I'd say that their manuals are only marginally better than Dwyer/Love, their tech support is great.

If you learn something from talking to them, I'd like to know it as well so I can learn.

I totally agree with you. I would have thought that you would expect a large thermal mass like that to provide significant damping and thus avoid overshoot. But I experienced a case just two days ago where I set the temp to 44F, and it overshot to 38F. But I think it's becase that was the first time I used a thermowell. I think it's a "momentum" effect. The outer parts of the vessel reach 44 earlier, and heat continues to leave from the center where the thermowell is. So by the time the center sees 44, the outer parts are cooler and more heat can escape, bringing the center below 44. So the whole mass coasted to 38.

I think I need to set my hystersis tighter.

Hex23 said:

I totally agree with you. I would have thought that you would expect a large thermal mass like that to provide significant damping and thus avoid overshoot. But I experienced a case just two days ago where I set the temp to 44F, and it overshot to 38F. But I think it's becase that was the first time I used a thermowell. I think it's a "momentum" effect. The outer parts of the vessel reach 44 earlier, and heat continues to leave from the center where the thermowell is. So by the time the center sees 44, the outer parts are cooler and more heat can escape, bringing the center below 44. So the whole mass coasted to 38.

I think I need to set my hystersis tighter.

Click to expand...

Yep, this is also why most HBT'ers seem to recommend taping your thermocouple to the outside of the keg vs the center of the thermal mass (aka thermowell). You might want to give that a try. It might kick the freezer on a few times to cycle and settle the temps, but I think this is probably better than overshooting.