Anyone know a cheap PID with analog output?

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kshuler

kshuler

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Hi everyone-

i am attempting to go bonkers and modulate the flow rate of my wort through the plate chiller so I can get to a specific wort temp directly into the fermentor as fast as possible. I know there are actuated valves that are more than just open or closed, but can be opened to variable degrees by applying a varying voltage.

The only question is this- all the PIDs that i know output a digital on off signal to an SSR or a contactor, which would not allow control of these valves. Does anyone know where I could get a relatively cheap PID that has analog output (preferably 0-10 volts)? I have seen one that is quite cheap that can put out 0-20 mA, but not varying the voltage, and I don't think this would control a 0-10v actuator. Is there a way to convert the 0-20 mA variable output to 0-10 volt output? The cheapest valves I have seen that are modulating are voltage modulated, not current modulated.

Klaus
 
Are you saying you DID find one that provides a variable current output?

If so, I believe you can build a current controlled voltage source with a few simple electronics parts.

I'm digging WAY back in my brain for this, but I think a couple of op-amps can do it.

Let me look at some old college texts to see if I have an example.
 
Walker said:
Are you saying you DID find one that provides a variable current output?

If so, I believe you can build a current controlled voltage source with a few simple electronics parts.

I'm digging WAY back in my brain for this, but I think a couple of op-amps can do it.

Let me look at some old college texts to see if I have an example.
Click to expand...

Yes, I found one PID for $69 that will do 0-20mA output, but the valve I ordered requires 0-10 volts DC for proportional control. It seems to me back in my high school electronics days that V=IR... so maybe a resistor might work, but the problem is I have no idea what voltage the 0-20mA signal is or what size resistor to put in line. Also, does the PID vary the voltage or the resistance to change the current from 0-20 mA?

As it turns out, after looking for a long time today I seem to have found something that will give 0-10 v, but it is $100. It is a love controls 16B-63. The other option is the 16B-62, which also offers "voltage pulse output" instead of SSR output, but I have absolutely no idea what voltage pulse output would mean.

Op-amp.... wow. Seems fairly advanced for my meager electronics skills. I had to look up what they were, but it sounds like they are little computer circuits. If you find some way to convert the signal I would be very interested!

Thanks.

Klaus
 
All that is needed is a 500 ohm resistor, 20MA through 500 ohm = 10 volts drop, this is similar to what we do with 4-20MA signals in PLC's with a 250 ohm resistor to get a 5 volt signal. The PID varies the current in the loop, usually with a 24VDC supply driving the loop so it can handle up to 600 ohm loads.
 
I don't think it's going to be that simple.

I gree that putting the resistor on there will show you a variable voltage drop across that resistor, but the problem is that once you connect the valve he wants to control, the resistance seen by the PID changes.

Also, I don't know if there will be enough current available to even operate thew valve. That PID will limit the current.

Might have to use op-amps or something, along with another DC supply, to get a proper driver for the motor that can provide the current the valve needs.
 
The ones we used were selectable for Voltage or current on both input and output with a zero and span adjustment so you could set to whatever you wanted for range. They were 120VAC powered units.

Not sure what kind of current your proportional valve needs.

edit Our use was 4-20ma to 0-10 vdc.
 
kshuler said:
The other option is the 16B-62, which also offers "voltage pulse output" instead of SSR output, but I have absolutely no idea what voltage pulse output would mean.
Click to expand...

Voltage Pulse Output is used for SSR and SCR Switch style power conductors that are used in Heat control systems.

Pulse output is a time based proportional output. Duty Cycle ie. Percent of time on vs percent of time off.

The 4-20 and 0 - 10 outputs are Magnitude proportional devices. The outputs are typically used with Phase Angle SCR power controls.
 
kshuler said:
Yes, I found one PID for $69 that will do 0-20mA output, but the valve I ordered requires 0-10 volts DC for proportional control. It seems to me back in my high school electronics days that V=IR... so maybe a resistor might work, but the problem is I have no idea what voltage the 0-20mA signal is or what size resistor to put in line. Also, does the PID vary the voltage or the resistance to change the current from 0-20 mA?

As it turns out, after looking for a long time today I seem to have found something that will give 0-10 v, but it is $100. It is a love controls 16B-63. The other option is the 16B-62, which also offers "voltage pulse output" instead of SSR output, but I have absolutely no idea what voltage pulse output would mean.

Op-amp.... wow. Seems fairly advanced for my meager electronics skills. I had to look up what they were, but it sounds like they are little computer circuits. If you find some way to convert the signal I would be very interested!

Thanks.

Klaus
Click to expand...

Go with the Voltage output Controller. You will be over the $100 by the time you get a signal conditioner to convert the 4-20 to voltage. With out the Valve specs, it would be hard to tell if the
output from that controller will have enough current or not.

Make sure you check the current capabilities
 
It sounds like a Belimo valve is going to be used for the proportional valve, which have a high impedance 0 - 10 VDC signal connection, and a separate 24VDC input for motor drive. Since I have 5 of these in my plc controlled brewing system and work with similar valves in industrial control installations the resistor method should work well as it is used for similar applications for converting current signals to voltages for inputs.
 
kladue said:
It sounds like a Belimo valve is going to be used for the proportional valve, which have a high impedance 0 - 10 VDC signal connection, and a separate 24VDC input for motor drive. Since I have 5 of these in my plc controlled brewing system and work with similar valves in industrial control installations the resistor method should work well as it is used for similar applications for converting current signals to voltages for inputs.
Click to expand...

Yeah I imagine the resistor would also work as Integral action from the PID will get the valve opened to the right flow regardless of whether the signal is scaled properly or not assuming its in the ball park. If the input is indeed high impedance, the losses that might cause span issues would be minimal.
 
Excellent, thanks! So it sounds like people have used a resistor successfully, then. A signal conditioner looks like it will bump the price well above the $100 mark. The two models of PID I have seen that are candidates are the Love 16B-63 and the Omega CN4316-F1-R2. Both controllers have dual outputs (SSR and 0-20mA for the Omega controller, and for the love controller it is SSR and selectable 0-5 and 0-10 volt). The price difference is 30 dollars, plus the cost and effort of converting 0-20mA output to 0-10v output.

I assume the 500 ohm resistor has to be wired in series, to convert the signal, right? How sure is everyone that it will work? I can probably wire a single resistor in series even with my meager knowledge, but is it really that simple? And how do you know that 500 ohm resistance is needed? Doesn't it depend on whether the circuit varies the voltage or the resistance of the circuit on what the converting resistor's value is? Can anyone explain the math of figuring out the resistance required?

At the moment I am leaning toward spending the extra 30 bucks to avoid the hassle, but could certainly be convinced otherwise. Always nice to save an extra 30 bucks.

Klaus
 
wire 2 - 1K 1/4W resistors together to hit 500 ohms, one end needs to be at - lead for valve and - output of controller, other end is where the valve signal line and + output of controller go. The Belimo valve still needs 24VDC to power valve motor on + connection of valve, - side of power supply goes to the - side of the valve. You can see a diagram on the Belimo website for the proportional actuators if you have difficulty with these instructions. The resistor method is not uncommon with the belimo and johnson control actuators and 4-20 MA controllers.
 
Looking a bit further, I suspect a simple resistor may not be the right answer. It seems there are entire product lines devoted to converting between 0-20mA output and 0-10v output. Here is an example: http://www.crouzet-usa.com/downloads/millenium/Input_Converter_Module.pdf

It seems to me that if it was as simple as a resistor then there wuld be no need for these kind of products, right?

Klaus
 
Actually the resistor method should work as the input to the valve is High Impedance as someone mentioned earlier. We use resistors all the time at work to convert 4 - 20 to a voltage. You end up with a zero offset using a resistor though. Still not a really big deal. Some of the controllers will allow you to set output to 0-20ma.

The conditioners are typically used if you want to have isolation and also have zero and gain adjustments. The resistor you have to size to get your span and endup with a zero offset.

I'd go with the 0-10 VDC PID and call it a day, but either should work.
 
Well, looks like the decision has been made. I put a bid on a Honeywell UDC3300 on ebay and just won for 36 bucks. This is a single output with 4-20mA signal, an alarm and a second "auxiliary output" that apparently can be set as a second 4-20 mA controller for cooling. The actuated valve can be set with a dip switch to either 0-10v or 2-10 v, so I imagine the resistor should still work well when switched to 2-10v mode. I think for 36 bucks, the UDC 3300 is a damned STEAL. Seems like a very capable (but overly complex) unit.

So, I guess in the end I will try to 500 ohm resistor method! Thanks everyone for your input. I'll try to wire it like in the Belimo diagrams (even though it is not a Belimo valve).

Klaus
 
please do a write up on your findings and a build if possible. Im sure others would like to see how you did it.

Good luck
 
kshuler said:
Well, looks like the decision has been made. I put a bid on a Honeywell UDC3300 on ebay and just won for 36 bucks. This is a single output with 4-20mA signal, an alarm and a second "auxiliary output" that apparently can be set as a second 4-20 mA controller for cooling. The actuated valve can be set with a dip switch to either 0-10v or 2-10 v, so I imagine the resistor should still work well when switched to 2-10v mode. I think for 36 bucks, the UDC 3300 is a damned STEAL. Seems like a very capable (but overly complex) unit.

So, I guess in the end I will try to 500 ohm resistor method! Thanks everyone for your input. I'll try to wire it like in the Belimo diagrams (even though it is not a Belimo valve).

Klaus
Click to expand...

Its great that they have the selection on the valve to change it to 2-10v. That solves the zero offset problem. Good luck
 
Man, I don't know why you chose to ignore kladue. If your PID has a 0-20mA output a 500 ohm resistor would have been perfect. I work for a company that specializes in data acquisition equipment and kladue's suggestion is perfectly valid.

The reason they have products like that is because they usually offer isolation as well. Isolation would be good if the signal is coming from an electrically noisy environment and you want to keep that noise out of your panel. Or they are used to repeat the signal if their is too much of a burden on the current analog loop.

Dont chase the bid on that thing too hard, you really dont need it.
 
CodeRage said:
Man, I don't know why you chose to ignore kladue. If your PID has a 0-20mA output a 500 ohm resistor would have been perfect. I work for a company that specializes in data acquisition equipment and kladue's suggestion is perfectly valid.

The reason they have products like that is because they usually offer isolation as well. Isolation would be good if the signal is coming from an electrically noisy environment and you want to keep that noise out of your panel. Or they are used to repeat the signal if their is too much of a burden on the current analog loop.

Dont chase the bid on that thing too hard, you really dont need it.
Click to expand...

I don't think I really ignored kladue, although I was not diligent in immediately looking at the actuator he mentioned. After that post I looked at the wiring diagram he pointed out (the Belimo LR24) and saw what he was talking about. Right in the instructions it showed, just like he said, a wiring diagram on how to convert from 0-20 mA to 0-10V. Obviously you guys have a LOT more knowledge than I do on this stuff (as does ANYONE who has done anything like this before-- I am a total noob to this kind of stuff), and I do put great value on what you all say. I plan to wire it exactly as Kladue showed.

As for the PID-- it is true that I don't need something as complicated as the UDC3300- it will be more difficult to program and understand than the lesser units, I think, but it is a screaming deal at 36 bucks, when the next option that would work is 69. At the price I got it it is less than the auber PIDs that I have , and still is by far the cheapest option I have seen for a PID with analogue output of any kind, especially with dial loop current control. I would rather have a 1/16 DIN unit and the UDC 3300 is a 1/4 DIN, but for the price I couldn't turn it down.

Thanks everyone for the help. I will try to write it up once everything arrives.

Klaus
 
Klaus, my apologies. I thought the auction was for a voltage to current loop converter.

I am interested to see as to how it integrates together, a valves change in surface area in relation to it's position is anything but linear. Well, unless it is a V profile needle valve. So the tunning on the PID is going to be interesting. I definitely think it would work and bet a bunch of HERMs brewers are waiting with baited breath for the results.

One last thing, you will want to set the valve to a 2-10V input if the output of the pid is 4-20ma.
 
whoops... just noticed something that may cause an issue... the valve I have (a honeywell M7410F) has input voltage as 24 volt AC... ALTERNATING current, but the control voltage is listed as 0-10v DC.... Can't really put a resistor between these two (alternating and direct), can you? Some valves seem to work on DC as well as AC, but I don't see this anywhere in the product manual. Output of the UDC3300 appears to be 4-20mA DC.

Klaus
 
HI CodeRage-- no problems! Ultimately I am planning in the distant future to switch to HERMS and a three vessel system, but not until I can move to a bigger house which is several years out. At the moment this is sort of a project looking for a reason to exist. I am using it as a learning tool mainly, but it is just going to control the rate of the wort outflow through my chiller so the wort heads to the fermentor at exactly the right temperature.

It actually is an interesting problem, I think. I will not be able to set the PID to cool, I don't think, and will have to have it control HEATING. If it was on a cool cycle, when it thinks the wort is too hot it will power the actuator, which will open the valve MORE, thus increasing the rate at which wort flows through the chiller, warming it up. This is the opposite of what the PID would expect and I think it would make it not work at all. If it works through the heating cycle, on the other hand everything should work well, I am just not sure how the thing will respond to overshoots... if it completely closes the valve at any time, then that will kind of defeat the purpose. At the moment I am thinkning of running a very small guage bypass tubing from before the valve to just past the valve. THis would allow a trickle of wort past the valve even if it is closed. Since the rate would be slow if the main valve is closed, it would be very cold wort and would actuate the valve again. The UDC controller also has a variable dead band setting, but I don't really understand this, but if it means I can make he valve NEVER completely close, then I can avoid a bypass.

I'll do some experimenting when it arrives.

Klaus
 
nah, you're fine. The 24VAC is the power the actuator needs to function, the control signal will still be DC. Find a doorbell transformer that puts out 24VAC with a 110VAC input and is capable of at least 1.4VA.

Edit.
The deadband is the space around the process variable (temp) +/- x degrees that the controller sees as good enough. Ie dont tweak the valve if you're only 0.1 degrees off and at a steady state.
 
Looking at the UDC3000 manual it should do anything you need. Its quite a capable controller to be honest. For $36 you might as well have stole it :).

Page 9 states the control signal can be set to direct or reverse action. So if the valve behaves in the opposite fashion you desire set it to reverse and the valve should work in 'cooling mode' if you will.
 
subscribed.

i have been pondering something like this to control the flow through my tankless heater. i would be able to just hit 'go' and get 170 degree water out and let it alter the flow rate for me, rather than having to tinker with a valve all of the time to get the temp right.
 
The ramp function is going to be an important part of the tuning as the time lag between control change and temperature change on start up can cause big temperature and control output swings as the controller settles.
 
Thanks for pointing out the reverse function from the manual. Perhaps I can have it on a cooling cycle after all and just reverse the action. That would seem to make more intuitive sense, as it is in fact controlling the flow of wort through a chiller. The manual is such a massive beast that I have to say I can't understand about 90% of it. That's the downside of getting such a complex controller. The price was right, though!

I didn't even consider that i might have to futz around with the ramping when it starts. I am used to using PIDs with heaters (I wired a PID for fermentation control to control a few brewbelts based on a thermowell RTD sensor for winter use) and don't have any experience controlling valves. The way plan to use it is with heating control, so when the temp gets too cold, the PID sends a signal to open the valve a bit more and heat it up. I think I figured out a way around the bypass valve that I had planned, too. I just need to turn on the cooling source for a while during recirculating (I clean by recirculating boiling wort for 15 minutes), and not turn power onto the valve until the wort is already running cool. The valve takes some time to open (not sure how long), and I presumed that, since the PID can send signals quite frequently of how much to open the valve, it should stabilize rapidly. Guess not though, huh. So would you set a ramp to start at like 55 degrees (approx groundwater temp in early summer) and then over 1 minute ramp it up to 68 or whatever the recipe calls for?

And if anyone knows, I assume that reversing the action on the PID controller would allow me to put it in cooling mode, as it would basically turn the valve into a "normally open" type. Is there an advantage one way or the other. Seems to me with a proportional valve it should be able to do the same thing whether set to heating mode or cooling mode because it is trying to hit whatever value you set. Am I wrong?

Attached is the flow diagram I plan to use, or something like it, at least. I will have to modify the 3 way T valves to turn 360 degrees around so I can use them as a stopcock- off to the direction the handle points. This setup lets me do a lot of things with the system (RIMS recirc, recirc boiling wort to sterilize equipment, either chill the whole wort volume or use hopback and chill only when going to fermentor).
amku2i
 
kshuler said:
Thanks for pointing out the reverse function from the manual. Perhaps I can have it on a cooling cycle after all and just reverse the action. That would seem to make more intuitive sense, as it is in fact controlling the flow of wort through a chiller. The manual is such a massive beast that I have to say I can't understand about 90% of it. That's the downside of getting such a complex controller. The price was right, though!

I didn't even consider that i might have to futz around with the ramping when it starts. I am used to using PIDs with heaters (I wired a PID for fermentation control to control a few brewbelts based on a thermowell RTD sensor for winter use) and don't have any experience controlling valves. The way plan to use it is with heating control, so when the temp gets too cold, the PID sends a signal to open the valve a bit more and heat it up. I think I figured out a way around the bypass valve that I had planned, too. I just need to turn on the cooling source for a while during recirculating (I clean by recirculating boiling wort for 15 minutes), and not turn power onto the valve until the wort is already running cool. The valve takes some time to open (not sure how long), and I presumed that, since the PID can send signals quite frequently of how much to open the valve, it should stabilize rapidly. Guess not though, huh. So would you set a ramp to start at like 55 degrees (approx groundwater temp in early summer) and then over 1 minute ramp it up to 68 or whatever the recipe calls for?

And if anyone knows, I assume that reversing the action on the PID controller would allow me to put it in cooling mode, as it would basically turn the valve into a "normally open" type. Is there an advantage one way or the other. Seems to me with a proportional valve it should be able to do the same thing whether set to heating mode or cooling mode because it is trying to hit whatever value you set. Am I wrong?

Attached is the flow diagram I plan to use, or something like it, at least. I will have to modify the 3 way T valves to turn 360 degrees around so I can use them as a stopcock- off to the direction the handle points. This setup lets me do a lot of things with the system (RIMS recirc, recirc boiling wort to sterilize equipment, either chill the whole wort volume or use hopback and chill only when going to fermentor).
amku2i
Click to expand...

That is a great looking setup :mug:

Regarding your question on how long the valve will take to open will depend on what the settings for proportional gain and integral are. Integral really determines often it makes a valve adjustment to reduce the error between the measured and the setpoint.

Not sure if that controller has a auto tune or not but you may want to run a few tests with water and let the auto tune do its thing. PID gains may also change depending on flow rates. Its possible to get middle of the road gains that will cover a large range of flows.

You may want to auto tune at multiple flows to see how it responds. Good luck. It sounds like you'll end up with a really trick setup :)

edit: Yes, if the controller has both actions then you could heat and cool with the same controller. It complicates things a tad and may require slightly different gains however very doable.
 
regarding the use of ramping. You may want to use it. If you turn the controller on without ramping, you end up hammering the Controller with a huge error in the beginning. Depending on the response of the system, you could end up with Integral windup. This can cause large overshoots as the system tries to come into control

Derivative can also be used to minimize overshoot. It may take a while to get the gains set for your system, so a couple run throughs with water will help. I didn't read the manual but most controllers have auto tune these days and can help minimize the screwing around generating the right gains.
 
A suggestion would be to move the proportional valve to the coolant circuit instead of the wort circuit as it would not catch hop and cold break particles which would be a sanitation "oops" later. As to auto tune, it may or may not work, it depends on the response time to coolant flow change and time to transit heat exchanger to see response at temperature sensor. It is going to be interesting to see how this works as it can not be simulated and tuned before operation.
 
Well, thanks everyone for the advice. I will wait until I get all the parts and then give it a whirl. I have 2 brew days coming up this week, but I won't be ready yet to use the setup. It will probably be a month or more before I get the chance again, and I will update as things happen.

Again, thanks everyone!

Klaus
 
kshuler said:
Well, thanks everyone for the advice. I will wait until I get all the parts and then give it a whirl. I have 2 brew days coming up this week, but I won't be ready yet to use the setup. It will probably be a month or more before I get the chance again, and I will update as things happen.

Again, thanks everyone!

Klaus
Click to expand...
Stumbled over you [very] old thread. Did this end up working for you? I was hoping the tread ended with with your build/wiring/programming. Thanks, Jim
 

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