What is PID

[dondiego]

PID = Performance Indication Device. Used to determine when your water filter has exceeded it's life expectancy. If the red light comes on, change out your filter. If you use it on your lead pot and the light comes on, you need to get new alloy.

[BattleRife]

I will use this thread to air my opinion that the term PID is misused around here. The thing we are talking about is a PLC, Programmable Logic Controller. Proportional-Integral-Derivative (PID) is essentially an adjective to describe what specific type of PLC people are using to aid their casting.

[bangerjim]

Buy one. You will sware by it. They are wonderful on pots and heat treating ovens just to name two.

Buy one......you will swear AT it! All those wires and cords hanging off your pot and casting table. Not worth the danger and mess.

And tuning a PID controller CORRECTLY (!!!!!) is not that easy. I sell them..............and do not use one! Don't even use a pot thermometer. Just good old school of hard knocks knowledge and observation.

banger

[bangerjim]

I will use this thread to air my opinion that the term PID is misused around here. The thing we are talking about is a PLC, Programmable Logic Controller. Proportional-Integral-Derivative (PID) is essentially an adjective to describe what specific type of PLC people are using to aid their casting.

A PLC has programmable starts & stops, ramps and soaks and uses ladder logic. And rarely has any type of integral digital process display. They are generally rack-mounted and tie into a back-plane buss that talks to a main mother module and separate 24vdc power supply.

That little cheap thing most people on here are using is a simple cheap toy.......AND it is a prop-int-dir CONTROLLER, not a PLC. You need a computer to program a PLC. And the software to do it!

bangerjim

[bangerjim]

PID = Performance Indication Device. Used to determine when your water filter has exceeded it's life expectancy. If the red light comes on, change out your filter. If you use it on your lead pot and the light comes on, you need to get new alloy.

Wrong industry! We are talking temperature control here not water quality!

PID to us is proportional-integral-deravitive, the mathematical functions and gain/feedback factors used to tune and run a control loop, in this case temperature. They can be used to control pressure, temp, flow, level, just about anything in modern industry.

But not what you described. That is a unique product designed and built for the water industry and works on back pressure and conductivity.

banger

[bangerjim]

Plug the electrical cord into the PID and put probe in pot

A little more involved. You have to have a box to put the controller in, all the wiring and know how to hook it up, a plug on the box wired to the correct PID terminals (it ONLY has screw terminals in the back!) to plug your pot into, iso-thermic plug for the t/c wire to plug in, t/c wire/mounting for your pot, and a t/c. And then figure out how to tune the thing properly to control accurately. And then have wires running here & there on your casting bench connecting all that stuff up.

If you are an engineer, or have significant experience in building, wiring and configuring electronic gadgets, you will be just fine.

There are expensive but pre-built products on here somewhere that are "plug-n-play". But someone else has spent the time and money building it for you.

I do not use a controller and get perfect boolits. Never have.....never will. And I sell these things...basically free to me...including all the bells & whistles.


I certainly do not want to discourage stout-hearted people out there to do this, but I am a graduate process engineer, know all the in's and out's of process control and wiring, and still do not have/want one! Best bet is to buy a pre-configured set-up.......if you want to spend the money.

banger

[lwknight]

Jim , you make it sound almost scary trying to set up a pid controller.
Its not that hard to build one. I mounted everything to the back splash on my work bench. No box. I could put a cover around it if I cared that much for aesthetics I guess.
I spent about $70.00 bucks and 30-40 minutes wiring it up and good to go.
I used a 24v transformer and contactor.
The controller passes 24v to the contactor and the contactor passes 110 to the pot.

[Hardcast416taylor]

Gentlemen all. I wish to thank all of you for answering this old mans query about this device. Seeing as how I have been casting for over 50 years without such a device I have come to the conclusion that I`ll stay casting the same way I always have, without this "thing".Robert

[Pakprotector]

Proportional-Integral-Derivative

Correction signal is proportional to difference between set point and measured value. Integral...control signal is based on a time integration of the diff between set point and measured value. Derivative...control signal is based on rate of change between measured value and set point.

Now since this beastie only turns the mot from ON to OFF I am having issues believing it is truly PID...but I have no idea just how it decides to turn it on and off and how often it does that.
cheers,
Douglas

[felix]

You answered your own question in your first paragraph. That is why setting the parameters during the desired time interval is called calibrate. ALL auto-control devices, PID inclusive or not, need to have a personal interaction set-up. Go figure the complication involved in setting parameters for a car's engine, considering the different drivers and how often calibration takes place. Not to mention wear and tear on the hardware sensors and drivers. ... felix

[lwknight]

Now since this beastie only turns the mot from ON to OFF I am having issues believing it is truly PID...but I have no idea just how it decides to turn it on and off and how often it does that.
cheers,
Douglas

Its smart. It learns. It predicts.

[bangerjim]

Proportional-Integral-Derivative

Correction signal is proportional to difference between set point and measured value. Integral...control signal is based on a time integration of the diff between set point and measured value. Derivative...control signal is based on rate of change between measured value and set point.

Now since this beastie only turns the mot from ON to OFF I am having issues believing it is truly PID...but I have no idea just how it decides to turn it on and off and how often it does that.
cheers,
Douglas

You are right. PID is normally used in analog PROPORTIOAL control loops where a 4-20 madc process variable (or t/c or RTD) supplies an input signal. The gain/reset/and rate (other names for P-I-D) are adjusted to provide a smooth ramp up/ramp down to and around a specific set point determined by the setting on the front of the box. The output then varies proportionally to the deviation from the set point. That output is an analog signal, normally 1-5VDC or 4-20 madc to control various industrial equipment. You can "dial in" integral and derivative into on-off control algorhythms, but they are not normally used.

What these little things used with the pots are doing is "proportional on-off" control by switching a solid-state relay on and off to the power to the pot. Not REALLY PID control, but you can mess with the three parameters try and tune it. I used to teach classes that lasted a week showing new engineers and field techs how to properly tune P+I+D on control loops for pressure, temp, flow, and level, among other industrial techniques.

What those little 1/16 DIN controllers are doing is rudimentary to real control, but that is all that is needed....simple on-off (like a solid state thermostat someone said above) control of the heating element.

I could go on for a long time on how to tune controllers! But I will not bore y'all~! I have done it or over 38 years. Started with pneumatic controllers in power plants and have moved to solid state stuff today, including PLC's.

banger

['74 sharps]

I'll pass on another piece of equipment to have for casting, and the mold temp will still be a variable with or without one.

[felix]

Don't forget pressure regulation of the pot's drop into the mold. Must include density of the lead giving best precision. ... felix

[popper]

PID is a device to get you lead melted as fast as possible without temp overshoot. It will also keep the temp accurately. It is not necessary but works well.

[lwknight]

I guess I could elaborate a little more on 1 detail often overlooked.
The common controller actually has 2 switch circuits. One of which is a low or high alarm that can couble as a contactor controller. It would be possible to set up parameters to include using the secondary (alarm) switch to operate 2 separate elements. We don't really need that though.

With a little engineering, you could have a heater that would kick in auxiliary heat when the temperature dropped off too much. eg: assaulting the pot with a large cold ingot.

I even contemplated using a dual heater setup for smelting. It would involve using 3 separate gas regulators and 2 solenoids to the burner.
Regulator #1 would burn a low maintenance flame.
#2 would be set with the solenoid with high pressure gas on the low alarm circuit.
#3 would be set medium pressure with the solenoid on the regular temp control circuit.

[MaryB]

PID's are also handy for turning chest freezers into a super high efficiency refrigerator. I run one for my solar setup.

[dondiego]

Wrong industry! We are talking temperature control here not water quality!

PID to us is proportional-integral-deravitive, the mathematical functions and gain/feedback factors used to tune and run a control loop, in this case temperature. They can be used to control pressure, temp, flow, level, just about anything in modern industry.

But not what you described. That is a unique product designed and built for the water industry and works on back pressure and conductivity.

banger

banger - It was a joke! .........

[bangerjim]

banger - It was a joke! .........

I know! But there are ACTUALLY control/monitoring devices that monitor the DP and conductivity across water filters (commercial/industrial, not home junk) that do exactly that!

banger