RIMS the concept?

[aamcle]

I've been brewing for some time and I'm about to ask some thing real dumb

As a background, Ive built and used a number of electric systems, my temperature probe has either been mounted in the bottom of the urn/kettle or in the wort return line of a recirculating BIAB.

In both these configurations the PID setup (auto tune) is dependent on the volume of wort and in the case of the recirculating BIAB the flow rate as well as the volume.

In the case with a RIMS were the temp probe is on the outlet of the heater assembly.

Its obvious that the PID setup is dependent on flow rate through the heater assembly but is it also dependent on the volume of wort and the effects of grain additions?

Or to put it another way, if I had a RIMS setup on the side of my BIAB would it matter how much wort I had in the URN.?

I take it I'd need a powerful ULD heating element to make this work?

Atb. Aamcle.

 

[PlexVector]

RIMs requires that the temp probe is at the output of the RIMS tube because the volume of wort in the tube is small and you risk overheating or boiling in the tube.

But to answer your question in a word, no.

RIMs and HERMs are good at maintaining a set temp or increasing temps incrementally over longer time intervals, but not so much making large temp swings to a large mass in short intervals. (unless your just heating water, not wort), Too keep the wort "safe" it's a balance of flow rate versus element power as to how fast you want to heat the mass of wort in the kettle without scorching.

 

[aamcle]

Thanks that's what I wanted to know, I'll keep my probe in the Biab wort return line.


Regards. Aamcle

 

[PlexVector]

Thanks that's what I wanted to know, I'll keep my probe in the Biab wort return line.


Regards. Aamcle

I use a 120V RIMs on the mash tun and I found that I have to set the RIMS 2 degrees above the temp I want the mash to be at due to system heat losses. The flow rate is based on having it flow as quickly as possible without getting a stuck mash.

To auto tune the PID I used just water and preheated to 140F which is the low end of mashing and then let the PID auto tune to bring it up to 152F with the lid off the cooler for max heat loss and a flow rate that looks like what I would be using during mashing and not get a stuck mash. And that got it in the ball park and has worked out pretty good regardless if the set temp is in the range between 150 to 156.

As a side note, I use the RIMS during CIP to keep the PBW hot (set and forget) rather than fiddling with propane.

 

[thekraken]

I use a 5500watt/240volt element at 120volts, that works out to 1375watts. I have a temperature probe that monitors the temperature of wort flowing into the tube as well as a probe monitoring temperature flowing out of the tube. Like PlexVector I typically experience about a 2 degree difference between these probes while maintaining temperature.

I would say that PID performance does depend on the mass of the mash. BUT I'm guessing that an autotune at your typical mashing 'conditions' will be good enough to cover the range of mashing conditions in your system.

 

[augiedoggy]

This was the reasoning for a longer lower watt density element in my rims... I can set the flow rate low at 1.5-2gpm and the wort coming out of the other end of my rims is consistently heated to an even temp (my setpoint once things stabilize) I dont have to worry about any denaturing or scorching this way.
I lose 1 to 2 degrees between rims outlet and MT outlet also depending on room temps.

 

[augiedoggy]

I use a 5500watt/240volt element at 120volts, that works out to 1375watts. I have a temperature probe that monitors the temperature of wort flowing into the tube as well as a probe monitoring temperature flowing out of the tube. Like PlexVector I typically experience about a 2 degree difference between these probes while maintaining temperature.

I would say that PID performance does depend on the mass of the mash. BUT I'm guessing that an autotune at your typical mashing 'conditions' will be good enough to cover the range of mashing conditions in your system.

I disagree here... As long as the control temp probe is at the rims outlet I believe the autotune would be more effected by the rate of flow not the amount of liquid being heated... I do 5 and 11 gallon batches as the same rate of flow and the single autotune was all that was needed...

 

[thekraken]

I disagree here... I believe the autotune would be more effected by the rate of flow not the amount of liquid being heated... I do 5 and 11 gallon batches as the same rate of flow and the single autotune was all that was needed...

But that's what I was sayin sorta

Per the original question I'm saying the mass of what's being heated has to effect the performance of the PID algorithm. I'm just saying that for our little home brew systems it's not a big deal. The nature of the 'learning' PID algorithm allows it to compensate for sub-optimal tuning too.

 

[augiedoggy]

But that's what I was sayin

Per the original question I'm saying the mass of what's being heated has to effect the performance of the PID algorithm. I'm just saying that for our little home brew systems it's not a big deal. The nature of the 'learning' PID algorithm allows it to compensate for sub-optimal tuning.

If the flow is low enough and power strong for the rims to more effectively "reach and manipulate the control point" the mass of the amount of liquid being maintained is irrelevant.
Once the mash temp is close enough and in the temp window where the rims has enough power to completely manipulate and control the output temps (and this is were the autotuning program really does its magic ) The mass of liquid or mash in the MT will have no effect on performance of the PID or rims...

To me it seems some people use their rims in a less effective way.. They use more flow than the element/rims configuration can evenly and steadily control/ manipulate and so they will have inconsistent results that will vary more with mass (which can ultimately effect flow rate in this case due to a thicker grainbed or more plugged false bottom when its the limiting/varying factor.).. Just my theory on it anyway after multiple rims setups and flow experiments... Someone with more engineering knowledge on this could probably explain it clearer.

 

[PlexVector]

If the flow is low enough and power strong for the rims to more effectively "reach and manipulate the control point" the mass of the amount of liquid being maintained is irrelevant.
Once the mash temp is close enough and in the temp window where the rims has enough power to completely manipulate and control the output temps (this is were the autotuning program really does its work The mass of liquid will have no effect on performance of the PID or rims...

To me it seems some people use their rims in a less effective way.. They use more flow than the elements can evenly and steadily control/ manipulate and so they will have inconsistent results that will vary more with mass (which can ultimately effect flow rate in this case due to a thicker grainbed).. just my theory on it anyway..

Agreed. RIMs system is only affected by the mass flow rate and temp differential of the input to output of the RIMs. It has no concept of the mass any where else.

 

[thekraken]

Agreed. The mass of the liquid inside the RIMS tube is the same whether you have 10 gallons or 20 gallons inside your mash tun. But the performance of the system as a whole will certainly be effected by the mass of the mash.

(Let me take a step back here and mention that my RIMS tube uses custom sort of a cascade control algorithm rather than the standard off the shelf PID box that most of us use. The off the shelf PID box is certainly good enough for great beer, but if a control algorithm *could* consider more variables, such as the mash's mass, I contend that the controller could perform better.)

 

[JonW]

I've always felt that measuring the output of a RIMS system to determine your actual mash temperature is an imprecise activity. What does the temperature of what is coming out of your RIMS tube have to do with the actual temperature of what is in your mash tun? Nothing!

In most of these configurations, the PID algorithm is trying to hit a target that you've set on the exit of your RIMS system. I believe there is some trial and error in getting a proper flow rate that allows sufficient heating (but not too much). When run long enough, the temp in the tun should eventually be getting to the temp of the output of the RIMS tube, but since most aren't measuring the MLT, it is imprecise.

Yes, I also measure the output of my direct fired RIMS system, because that is the only way I have to do it. My new build has temp probes both in the MLT and at the RIMS output, so I'm going to start experimenting and logging the differences in the two.

 

[BrunDog]

I consider the temp measured at the exit of my MT to be my mash temp. The RIMS tube temp is just there to get the rims temp in place and hold it steady. Per the other thread, there will be a 1-2 degree difference.

 

[augiedoggy]

Agreed. RIMs system is only affected by the mass flow rate and temp differential of the input to output of the RIMs. It has no concept of the mass any where else.

Yes True I forgot about that ... This is what I like about using a round solid 5/8 diameter element surface in a 1" ID rims tube... the heating element exposure to the mass of liquid flowing through it is increased and therefore increases efficiency and consistency of the exiting liquid temps.

if someone to use a 2" diameter rims tube the exiting liquid temps would most likely be inconsistent unless the flow was very very low and the liquid was really being mixed up in the rims well since otherwise more liquid would pass through without direct heat exposure.

 

[mabrungard]

This was the reasoning for a longer lower watt density element in my rims... I can set the flow rate low at 1.5-2gpm and the wort coming out of the other end of my rims is consistently heated to an even temp (my setpoint once things stabilize) I dont have to worry about any denaturing or scorching this way.

Caution. My old RIMS had only 1500w of power, but I still managed to denature my wort when I operated the system without a PID. I learned the hard way that having something that further moderates the power input to the wort is still valuable. I think even 1000w would have screwed me up when I was just operating with an on/off switch.

Monitoring the actual wort temperature immediately downstream of the heat source is a very good idea. (it only cost me a couple of batches before I figured that out). I never scorched the wort though.

 

[PlexVector]

I've always felt that measuring the output of a RIMS system to determine your actual mash temperature is an imprecise activity. What does the temperature of what is coming out of your RIMS tube have to do with the actual temperature of what is in your mash tun? Nothing!

In most of these configurations, the PID algorithm is trying to hit a target that you've set on the exit of your RIMS system. I believe there is some trial and error in getting a proper flow rate that allows sufficient heating (but not too much). When run long enough, the temp in the tun should eventually be getting to the temp of the output of the RIMS tube, but since most aren't measuring the MLT, it is imprecise.

Yes, I also measure the output of my direct fired RIMS system, because that is the only way I have to do it. My new build has temp probes both in the MLT and at the RIMS output, so I'm going to start experimenting and logging the differences in the two.

Ideally there is a PID to control the RIMs based on the output of the RIMS and a PID to control the set point of the RIMs and/or flow rate based on the Mash temp. Or something like that.

Don't make me go look for my controls theory and thermodynamics books in the attic...

 

[aamcle]

I usually auto tune with the volume in the urn that I plan to use, it works except that I do a lot of 1/2 size batches and the Rye batch that was a disaster.

It was an all Rye, I did a beta-glucan rest and still suffered a stuck mash which is an achievement in a BIAB needless to say most of the liquid stayed in the bag and temperature control went to bits.

My concern is that variable effect of the grain in the mash, holding water and changing the flow rate undermines the auto tune mostly it's been OK it's really only the Rye that messed up.

Have you tried auto tuning during the mash? My PID has the facility to limit the temperature overshoot during auto tune.


Atb.. Aamcle

 

[augiedoggy]

I've always felt that measuring the output of a RIMS system to determine your actual mash temperature is an imprecise activity. What does the temperature of what is coming out of your RIMS tube have to do with the actual temperature of what is in your mash tun? Nothing!

In most of these configurations, the PID algorithm is trying to hit a target that you've set on the exit of your RIMS system. I believe there is some trial and error in getting a proper flow rate that allows sufficient heating (but not too much). When run long enough, the temp in the tun should eventually be getting to the temp of the output of the RIMS tube, but since most aren't measuring the MLT, it is imprecise.

Yes, I also measure the output of my direct fired RIMS system, because that is the only way I have to do it. My new build has temp probes both in the MLT and at the RIMS output, so I'm going to start experimenting and logging the differences in the two.

Well unless you have some serious temp losses due to an unheated mashtun being outside in very cold temps it the temp of the exiting rims has everything to do with it... Its the only way you can effectively prevent any OVER heating of the mash and temp swings. and they usually have a consistent differential of 1-2 degrees this way.

Your going to have a degree or two loss from the MT and plumbing after the rims but measuring temps here provides the best/tightest control over overall wort temps, this is totally normal and can consistently be adjusted for....
If you have any flow variations the pid can more effectively compensate without "overheating" the wort inside the rims and causing large temp swings in the mash in the beginning of the mash process... This is why using a probe at the exit of the MT to control the temp in the rims tube is a bad idea compared to measuring and controlling liquid temps directly at the output of the rims. You will get some serious time delay and temp swings this way. I also learned this the hard way doing it the other way with my herms setup.

 

[thekraken]

@aamcle As PlexVector and others are saying, with a standard PID controller that I'm assuming you are using you only need to autotune to the flow rate you plan to use during the mash.

I apologize for complicating things earlier.

 

[augiedoggy]

Caution. My old RIMS had only 1500w of power, but I still managed to denature my wort when I operated the system without a PID. I learned the hard way that having something that further moderates the power input to the wort is still valuable. I think even 1000w would have screwed me up when I was just operating with an on/off switch.

Monitoring the actual wort temperature immediately downstream of the heat source is a very good idea. (it only cost me a couple of batches before I figured that out). I never scorched the wort though.

I use a PID... I wouldnt consider not doing so. but less watt density also has a huge impact on this hence a longer element which give more contact time with the wort and gentler heating exposure. This allows the rims to have the benefits of the herms without the drawbacks.

 

[thekraken]

Caution. My old RIMS had only 1500w of power, but I still managed to denature my wort when I operated the system without a PID. I learned the hard way that having something that further moderates the power input to the wort is still valuable. I think even 1000w would have screwed me up when I was just operating with an on/off switch.

Monitoring the actual wort temperature immediately downstream of the heat source is a very good idea. (it only cost me a couple of batches before I figured that out). I never scorched the wort though.

If you wouldn't mind elaborating I'd like to know a little bit more about what you were doing. You said you were using an on/off switch. Where in the system did you monitor the temperature? What kind of delta were you seeing between the RIMS output and the mash? How were you deciding when to flip the switch on/off? How did you determine that you denatured the enzymes, simply because you weren't getting conversion, poor efficiency, poor attenuation, etc?

(I'm interested in how that control algorithm worked inside your head)

 

[JonW]

Well unless you have some serious temp losses due to an unheated mashtun being outside in very cold temps it the temp of the exiting rims has everything to do with it... Its the only way you can effectively prevent any OVER heating of the mash and temp swings. and they usually have a consistent differential of 1-2 degrees this way.

Your going to have a degree or two loss from the MT and plumbing after the rims but measuring temps here provides the best/tightest control over overall wort temps, this is totally normal and can consistently be adjusted for....
If you have any flow variations the pid can more effectively compensate without "overheating" the wort inside the rims and causing large temp swings in the mash in the beginning of the mash process... This is why using a probe at the exit of the MT to control the temp in the rims tube is a bad idea compared to measuring and controlling liquid temps directly at the output of the rims. You will get some serious time delay and temp swings this way. I also learned this the hard way doing it the other way with my herms setup.

I didn't say it doesn't work, just that it is very imprecise and takes more than just the PID tuning to get an effective working system. Yes, I agree you must have the temp probe on the RIMS output to avoid overheating, but if you're not heating it enough over your desired setpoint, getting the actual mash temp to move may be a futile effort.

I often have 40-50 lbs of grain in my mash tun. While that in itself is a good insulator of temperature, it can also be hard to effectuate a change in a timely manner.

 

[aamcle]

To check I may have misunderstood something.

Scenario :- I have a RIMS tube with the temp probe on the outlet, a constant flow rate, water at strike temperature and I them mash in. The system is a recirculating BIAB returning the sweet liquor through the RIMS tube to the top of the bag/mash. I'm using the RIMS to maintain temperature and step mash, obviously wrt the bulk of the liquor its a ramp not a step.

If the flow rate remains constant can I expect the heated liquor leaving the RIMS tube to be at the set value irrespective of the volume of liquid in the mash tun?

The bag is in a basket so there is liquid under it and between the the wall of the basket and the wall of the urn, its a common configuration for recirculating BIAB.

If the bag was to effectively hold/retaining/slowly diffuse the returning liquor I might in practice be mainly recirculating the liquid surrounding the bag would RIMS still return the set point temperature to the top of the mash?



Thanks. Aamcle

 

[thekraken]

I'm using the RIMS to maintain temperature and step mash, obviously wrt the bulk of the liquor its a ramp not a step.

If the flow rate remains constant can I expect the heated liquor leaving the RIMS tube to be at the set value irrespective of the volume of liquid in the mash tun?

Yes, as long as the incoming temperature is within a certain range of your setpoint.

 

[alphaomega]

It seems the consesus in this thread is that the volume in the tun does not matter. That is not entirely true.
The PID algorithm does have an integral term (the I in PID), and the volume in the tun will be buffering the change. Now, for all intents and purposes, it probably does not matter, as you are not gonna do a half gallon mash, and if the volume is 4 gallons or 8, it will still be so slow to react that the PID easily copes.

The PID controllers are cheap and readily available, but if I were to implement my own control, I'd rather use fuzzy logic. PID works fine, but there is just no need for it, and auto tuning (or manual tuning) for different flow rates is no fun.
It is the mash temperature that you want to control, you just want 'sanity' out of the RIMS tube. Don't scorch and try not to denature enzymes, that's all. No need for temperature at the return to be within 0.1 deg.

 

[thekraken]

The PID controllers are cheap and readily available, but if I were to implement my own control, I'd rather use fuzzy logic. PID works fine, but there is just no need for it, and auto tuning (or manual tuning) for different flow rates is no fun.
It is the mash temperature that you want to control, you just want 'sanity' out of the RIMS tube. Don't scorch and try not to denature enzymes, that's all. No need for temperature at the return to be within 0.1 deg.

Another forum member (@BigBlock) came up with this formula that I've used successfully:

    calc_temp_diff=min(max_temp_diff, pid_output);                   //BIGBLOCK PID output reduces rims output temp as MLT temp nears the setoint
    rims_output_limit =( mlt_setpoint + calc_temp_diff - mlt_temp )  //Temp diff     (F)  BIGBLOCK - max_temp_diff changed to calc_temp_diff
                       * 1.0                                        //specific heat (Btu/(lb*F))
                       * flow_rate*8.3/60.0                         //flow rate     (lb/sec)
                       * 3600.0/3.412141                            //convert to wattage
                       / rims_wattage*100.0;                        //convert to % watts of my element

In other words given the flow rate of the liquid, and the power output of the heating element, we can just calculate what takes to heat from A to B. PID is used to compensate for inefficiencies, variances, heat loss, etc in the system. I hope to some day find time to refine this model to further reduce the need for PID.

 

[alphaomega]

@thekraken : yeah... and reduce the need to know the flow rate
I don't think it needs to be that hard (that's what she said). Say you have a tempsensor in the mash (Tm). And one at the output (To).
Then have a control loop of say one second.

IF Tm > SP THEN power = OFF
ELSE IF To < SP THEN power = HIGH
ELSE IF To < SP + 5 THEN power = MEDIUM
ELSE IF To < SP + 10 THEN power = LOW
ELSE power = OFF

SP of course being setpoint.
This is just basic concept, a real implementation should interpolate the output between conditions and it should not be this on/off, but even so, with one sec loop, i think even this would work reasonably well.

 

[BrunDog]

Well unless you have some serious temp losses due to an unheated mashtun being outside in very cold temps it the temp of the exiting rims has everything to do with it... Its the only way you can effectively prevent any OVER heating of the mash and temp swings. and they usually have a consistent differential of 1-2 degrees this way.

Your going to have a degree or two loss from the MT and plumbing after the rims but measuring temps here provides the best/tightest control over overall wort temps, this is totally normal and can consistently be adjusted for....
If you have any flow variations the pid can more effectively compensate without "overheating" the wort inside the rims and causing large temp swings in the mash in the beginning of the mash process... This is why using a probe at the exit of the MT to control the temp in the rims tube is a bad idea compared to measuring and controlling liquid temps directly at the output of the rims. You will get some serious time delay and temp swings this way. I also learned this the hard way doing it the other way with my herms setup.

10,000% agree.

-BD

 

[thekraken]

@thekraken : yeah... and reduce the need to know the flow rate
I don't think it needs to be that hard (that's what she said). Say you have a tempsensor in the mash (Tm). And one at the output (To).
Then have a control loop of say one second.

IF Tm > SP THEN power = OFF
ELSE IF To < SP THEN power = HIGH
ELSE IF To < SP + 5 THEN power = MEDIUM
ELSE IF To < SP + 10 THEN power = LOW
ELSE power = OFF

SP of course being setpoint.
This is just basic concept, a real implementation should interpolate the output between conditions and it should not be this on/off, but even so, with one sec loop, i think even this would work reasonably well.

I hear ya. The flow meter is in place as a safety measure any way so might as well utilize it.

 

[augiedoggy]

The flow meter is very useful for me to see the clarity of my mash as well as to be sure my false bottom/ filtering setup isnt plugged or my pump hasnt stopped... before I added the flow switch to my rims It was also there for safety reasons to ensure good flow and no chance of scorching...

I now caught another case of the bling bug and purchased a sightglass for the center of my rims tube totally not needed but helpful when sparging I guess or as a visual to see when my rims is flushed out or empty.

I seem to remember reading that the mypin pids do in fact have a "fuzzy logic" capability as well but im not 100% sure on that.
with my older rims configurations I did not autotune at all but for some reason with my latest design I found it performed a lot better without overshooting if I used the autotune to tune it and in all the batches since then I have never needed to touch it.

 

[ccfoo242]

Are there any PIDs that take the temp from two locations (heat location and mass location) and use both to heat the mass without this fudge factor to worry about? Seems like the PID algorithm was designed for a small closed system like a sous vide rather than a large, spread out system like we use.

 

[PeteNMA]

Don't forget that your enzyme activity is driven by the hottest temperature which the enzymes see. It's less important to heat the entire grain bed up to 152F or whatever temperature than it is to ensure that the liquor is being thoroughly recirculated.

 

[ryane]

Are there any PIDs that take the temp from two locations (heat location and mass location) and use both to heat the mass without this fudge factor to worry about? Seems like the PID algorithm was designed for a small closed system like a sous vide rather than a large, spread out system like we use.

PID loops are used on huge industrial systems to maintain temp, level, etc to a fraction of a percentage of the SP, you just have to be good at loop tuning, which very very few are, PID tuning is an art in of itself due in large part to the complexity of the processes we are controlling and lack on knowledge of how PID loops operate (laplace transforms etc)

You could easily insulate your lines and tun and help buffer against the heat loss (I prefer to mitigate process control issues with physical changes first), you can also do master/slave PID loops in a cascade to achive a MISO (multiple input, single output) PID loop, once you cascade loops though things become more complex and are more difficult to tune

 

[aamcle]

It's a lot easier to insulate measure the temperature loss, its about 1 Degree on my system, and add that to the set point so for example make it 66 not 65.

The effect of the incorrect value? over heating? what ever can be ignored we are making beer not err sorry can't think of a good example.
But if I could it would probably be something explosive that wanted to eat your face!

Aamcle

 

[alphaomega]

Yeah, that is the point. PID is total overkill for RIMS and they are tricky to tune.
But PID controllers are cheap and autotuning usually works well enough.

With my RIMS, I just used used a simple power controller. Mash in and try to hit my temperature, and set low power and low flow. If I gain a degree or two over an hour, I don't care.

 

[BrunDog]

Yeah, that is the point. PID is total overkill for RIMS and they are tricky to tune.

I disagree. PIDs, given ease of acquisition, cost, and installation are very appropriate. They are tricky to tune but most have autotuning. And even incorrect parameters will work.

Anyway not sure why this is much of a discussion. Put the probe at the top of the RIMs tube and measure it's output. Keep the flow reasonable and life is good.

 

[Bobby_M]

A lot of the shortcomings in PIDs have to do with the wide cycle times. It makes it difficult to use a powerful or overpowered RIMS element (in the case where you may want to ramp quickly). PIDs like Auber's 2342 have a cycle time of 2 seconds so even though you can program in a OUTH parameter to 10% or 20% output, it would pulse for .1 or .2 seconds and be off for 1.9 or 1.8 seconds. It would be great to have a PID that could easily modulate the max output power based on a 100 milisecond cycle. Then you could tune that thing perfectly based on your desired flow rate and you wouldn't get any oscillation (or not much) but you could still crank it for the mash out.

This is why I often rattle on about running a cheap PID in series with the Auber Power Regulator or a cheaper SSVR. I think of it like tuning a brutus 10 mash burner. You set the manual gas valve for how big the flame is and the controller turns it on and off.

 

[augiedoggy]

A lot of the shortcomings in PIDs have to do with the wide cycle times. It makes it difficult to use a powerful or overpowered RIMS element (in the case where you may want to ramp quickly). PIDs like Auber's 2342 have a cycle time of 2 seconds so even though you can program in a OUTH parameter to 10% or 20% output, it would pulse for .1 or .2 seconds and be off for 1.9 or 1.8 seconds. It would be great to have a PID that could easily modulate the max output power based on a 100 milisecond cycle. Then you could tune that thing perfectly based on your desired flow rate and you wouldn't get any oscillation (or not much) but you could still crank it for the mash out.

This is why I often rattle on about running a cheap PID in series with the Auber Power Regulator or a cheaper SSVR. I think of it like tuning a brutus 10 mash burner. You set the manual gas valve for how big the flame is and the controller turns it on and off.

Id really like to get a to a sure answer on this... Some people say the auber can be adjusted to work like the mypin does out of the box, Meaning it has a cycle time of 1 second... I did notice I had to autotune my rims pid when stepping up from a 1000w element to 1800w one... It works as it should now though, regardless of brewing batch size.

 

[BrunDog]

I don't think a cycle time of 2 sec is an issue. The element has a good bit of thermal mass in it so it is not going to have massive temp swings during a mash where the incoming liquid is a degree or two cooler than the exiting liquid.

The BCS goes down to one second but I do not believe it can accurately handle resolution less than about 20%. I have mine set at 3 secs (default) and it works great. I also sparge on the fly at 240VAC and with a fixed duty cycle the temp stays rock solid, and this is a massive temp difference (about 90 degrees).

 

[alphaomega]

I disagree. PIDs, given ease of acquisition, cost, and installation are very appropriate. They are tricky to tune but most have autotuning. And even incorrect parameters will work.

Anyway not sure why this is much of a discussion. Put the probe at the top of the RIMs tube and measure it's output. Keep the flow reasonable and life is good.

You obviously did not read what I wrote, and only quoted part of it.
You can disagree all you want, but it won't make it false. PID is not necessary to control a RIMS setup and it IS overkill.
The very next thing I said (which you chose to ignore) was that they ARE cheap and relatively easy can be made to work reasonably well. What I ment by that is that you might as well use a PID if you want. Sheesh.

A lot of the shortcomings in PIDs have to do with the wide cycle times. It makes it difficult to use a powerful or overpowered RIMS element (in the case where you may want to ramp quickly). PIDs like Auber's 2342 have a cycle time of 2 seconds so even though you can program in a OUTH parameter to 10% or 20% output, it would pulse for .1 or .2 seconds and be off for 1.9 or 1.8 seconds. It would be great to have a PID that could easily modulate the max output power based on a 100 milisecond cycle. Then you could tune that thing perfectly based on your desired flow rate and you wouldn't get any oscillation (or not much) but you could still crank it for the mash out.

This is why I often rattle on about running a cheap PID in series with the Auber Power Regulator or a cheaper SSVR. I think of it like tuning a brutus 10 mash burner. You set the manual gas valve for how big the flame is and the controller turns it on and off.

Well, I think you guys have 60Hz mains, right? An SSR only switches on/off at 0 volts (which is a good thing). At 60Hz, there are 120 zero volt crossovers per second, each half period being 8.333...ms long.
So, to have a 100ms cycle, means you can set the power from off to full power in only 12 steps (not entirely true, but close). That is not much resolution.
1 second is a fairly good trade off. The element in it self takes time to warm up and cool off also, so at some point you won't notice the cycling action at the output (though it might still be at 1 sec, but it depends on the setup).
Using the Auber power controller in series does not sound like a good idea and SSVR's are always a bad idea.