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(@pbruno3)
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Joined: 2 years ago
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February 17, 2019 12:39 am  

Great!

The wiring map notes should help guide. The letter codes indicate what each pin/port is capable of. Pins/ports marked with a 'D' can be digital inputs or outputs. Devices marked with a 'P' have PWM/Analog Output capability. But which it is is decided by the device element you set up in BruControl. Pins/ports with multiple capabilities can even switch to different modes by enabling/disabling device elements.

Per the note, "Duty Cycle and Hysteresis devices use a Digital Output (D).", so anything marked with a D can be duty cycle or Hysteresis. Period does not matter.

Per the note, "PID devices on pins with both Digital (D) and PWM Output (P) will use PWM Output. For binary switches (e.g. SSR), select pin without PWM Output (P)." which means that if a pin/port has PWM capability, PID will generate a PWM/Analog output, and if not, will generate a Duty Cycle output.

So, unless you are using devices which accept PWM or analog inputs, you should not use pins/ports that have PWM capability. For example, a standard SSR is a binary (on/off) device and will not accept a PWM signal. On the other hand, if you have a proportional device like a proportional valve or SSR, then use one with PWM. 


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(@oakbarn)
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Joined: 4 months ago
Posts: 62
February 17, 2019 4:38 pm  

I still do not understand PWM.  I thought I did.  Again most of my information is from my BCS build.  In that, PID, Hysteresis, and Duty Cycle were only available for the PWM Outputs of the BCS.  Because of that, I assumed that "PID, Hysteresis, and Duty Cycle"  were types of PWM.

 

What is confusing is that:

So, unless you are using devices which accept PWM or analog inputs, you should not use pins/ports that have PWM capability. For example, a standard SSR is a binary (on/off) device and will not accept a PWM signal. On the other hand, if you have a proportional device like a proportional valve or SSR, then use one with PWM. 

SSR in both cases?  Is there a Special SSR for PWM?     I tried google and did not find any answers.

So the real basic question, if using PID for a heating Element through an SSR, select a Pin

(Port) that is only "D"?    I was simply going to switch the Trigger Wire from my BCS PWM Output to one of the "P" Pins on the Arduino Mega and use the Device Type PID Control for my Device Element.   I am going to use all of the PINs i/o on the Mega but will have open "P" on the second Mega.   Should I reserve all of the "P" Pins on both Mega(s) since I do not really have any PWM widgets?

 

I am trying to formulate the transition wiring Plan from the BCS to BruControl.  The only hang up I have is understanding the PWM Pins and using them with SSRs.

 

 


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(@pbruno3)
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Joined: 2 years ago
Posts: 212
February 18, 2019 2:53 am  

PWM (Pulse Width Modulation) is a type of "variable" output, and that variation is based upon the net amount of time an output is on. Technically, and in the real electrical world, Duty Cycle and PWM are the same thing. In BC, PWM has a very fast cycle (1 kHz) and DC is very slow (>1 Hz). In BC, PWM cycle length is fixed, whereas you can set the cycle length for DC. Because the PWM happens so fast, it is not suitable for "slow switching" (relatively) devices such as normal SSR's (not proportional SSR's) but is suitable for fast devices like MOSFETs, transistors, etc. PWM is also suitable to convert to an analog signal via a low-pass filter (Resistor-Capacitor combination).

The bottom line is the calculated result from a PID is a variable amount (from none to full), and that output can be represented via a Duty Cycle (pins/ports with a D but no P) or a PWM (pins/ports that contain a P).

SSR is Solid State Relay - most normal models accept an ON or OFF input, and resultingly turn the output ON or OFF. These SSRs are inexpensive (say, < $30) and turn on and off within a handful of milliseconds, but when switching 60Hz AC current, will make a mess of it. Proportional SSRs (such as the Crydom MCPC) accept an analog input, and appropriately switch a 60Hz AC signal using various methods.

For comparison sake, the BCS does not have a PWM output - it has Duty Cycle output appropriate to drive normal SSRs.

As far as pin/port allocation, if using normal SSRs... only use pins/ports without a P. You can use other devices (like Duty or Hysteresis) on pins/ports with a P, just know if you use a PID, it will generate a PWM output, not a Duty Cycle one, which will cause a normal SSR to be ON or OFF unexpectedly.


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(@oakbarn)
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Joined: 4 months ago
Posts: 62
February 19, 2019 1:28 am  

So the BCS does not have a True PID.  Interesting.  When running a heating Element,   Should I use PID control on a "D" Pin  with a Standard SSR or choose Hysteresis with a small offset?   Not sure it would make much difference.  What I do is heat a HERMS Bath that I want that type of Precision.    The BCS keeps it within about .5 F of the Target.   Everything else I use Hysteresis anyway.  If I want True PID I would need a Proportional SSR.  On Ebay they have this one that is 40 amps.  

https://www.ebay.com/p/Douglas-Randall-SSR-Proportional-Controller-Crydom-RPC4840-RESISTIVE-Loads-NOS/1083256454

 

When I looked at the Crydom MCPC, the control signal is 8 to 32 vdc.

 

I think I will not be needing that precision regardless.

Air Force Precision:

Measure with a micrometer

Mark with Grease Pencil

Cut with Ax

 

 

 

 


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(@oakbarn)
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Joined: 4 months ago
Posts: 62
February 19, 2019 3:58 am  

What I think you were saying:

 

PID on a "D" is fine even with a cheap SSR.  Do not put PID Control on a "P" unless you have the proper Proportional SSR.


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(@pbruno3)
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Joined: 2 years ago
Posts: 212
February 19, 2019 4:59 am  

I don’t know the BCS’s algorithm. I personally used a 462 and believe it’s PID was accurate. 

In BruControl, for heating liquid, there is really no difference between a PID through a non-P capable pin and a binary SSR vs a PID through a P capable pin and a proportional SSR, so long as the cycle time is relatively short (say less than 2 secs). Use a PID to hold mash temp. You could use Hysteresis but depending on flow rate the lag may cause over and undershooting.

Again, proportional SSR has nothing to do with the PID algorithm - it calculates the same way, but a D only output results in a Duty Cycle Output and a P output results in a PWM output. Use a standard SSR connected to an output without PWM capability and you’ll be good!

 


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(@pbruno3)
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Joined: 2 years ago
Posts: 212
February 19, 2019 5:00 am  
Posted by: oakbarn

What I think you were saying:

 

PID on a "D" is fine even with a cheap SSR.  Do not put PID Control on a "P" unless you have the proper Proportional SSR.

Exactly!


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