solder pot controler

dbj

I am working on a preheater for a solution that use's a DS2760 thermocouple to measure the fluid as it leaves a 22" coil of copper wire. the wire is heated with a
microwave oven transformer , the primary coil is the imput and the high voltage coil was removed and replaced with two turns of large copper wire which feeds the low votage high current to the preheater's 22"·coil, supplying 0-120 amps like a big Weller soldering gun.The output·is controled now by a light dimmer switch.·I would like to be able to control the exact temperature of the fluid useing my BSPpx24 just like your custom solder pot, what method do you use to control the heating of the solder pot, Analog Input Power or potetiometer control. I know from the article that you use a Crydom SCR too feed the heater to regulate the set-point. That is what I would like to do also, but I am useing a Transformer to control the heat of the coil. Would it be best to control the primary coil with pwm or analog imputs. Thanks David

Chris Savage

Hello,
·
·· The way you control the heating element really depends on how it is connected as well as the method of control and feedback.· In the case of the solder pot it is set up much like a soldering station, which uses differential gap and a simple thermostat setting.
·
·· The Solder Pot Controller reads the current temperature of the pot and turns on the SSR to energize the pot whenever the current temp is lower than the set temperature.· The differential gap is adjustable, but typically it is a couple of degrees.
·
·· In this case it doesn’t matter since we’re using an SSR the pot can toggle on/off as fast as it wants and it will always try to hold the temperature.· PID is not used, so the only time it really overshoots is during initial startup and it is only by a few degrees.· The SSR is a Crydom capable of switching 50A.· I hope this helps.

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Chris Savage
Parallax Tech Support

dbj

Thanks, I see what your saying, the solder pot is one big mass, too cold heat on too hot heat off in the case of my application the liquid is constantly being feed past the coil.The way I have it set up now is by manually adjusting the dimmer to a setting that gives me 70 amps constantly going threw the coil. But the problem is that this setting wont always work because of temperature variations of the liquid. What I want to do is too be able to let the stamp adjust the current going threw the wire and maintain a constant output temp. So the coil on the transformer needs a initial start up setting and a delay followed by temp low increase amps temp high decrease amps. What is the best Type of SCR and method of controlling it resistance or voltage I would think from one volt full on to five volts full off.
Does any one Know of a similar process ? Thanks for the help David

Chris Savage

Dbj,
·
·· You could use current control, but with an SSR you’re going to get voltage on/off.· Which is fine for both differential gap as well as PID (See Andy Lindsay’s article in the Stamps In Class Forum).· This will also be easier to control from the BASIC Stamp since it’s merely an on or off state and the I/O pin can almost always directly drive the SSR input.· Take care.

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Chris Savage
Parallax Tech Support

dbj

Was trying to run IntegralAlgorithm.bs2 and change the line drive = i + offset MIN 650 MAX 850 and I get a syntax error Undefined symbol for the offset. I dont understand? tried running on BS2p and BS2 both dont work.
Thanks David

P,S is this OK?

' IntegralAlgorithm.bs2

' Demonstrates how integral control influences error correction

' in a feedback loop.




' {$STAMP BS2p}
' {$PBASIC 2.5}



SetPoint CON 0 ' Set point

Ki CON 10 ' Integral constant



Current CON 0 ' Array index for current error

Accumulator CON 1 ' Array index for accumulated error



sensorInput VAR Word ' Input

error VAR Word(2) ' Two element error array

i VAR Word ' Integral term

drive VAR Word ' Output



DO



DEBUG "Enter sensor input value: "

DEBUGIN SDEC sensorInput



' Calculate error.

error(Current) = SetPoint - sensorInput



' Calculate integral term.

error(Accumulator) = error(Accumulator) + error(Current)

i = Ki * error(Accumulator)



' Calculate output.

drive = i + offset MIN 650 MAX 850



' Display values.

DEBUG CR, CR, "ERROR", CR,

SDEC ? SetPoint, SDEC ? sensorInput, SDEC ? error(Current), CR,

"INTEGRAL", CR,

SDEC ? Ki, SDEC ? error(accumulator), SDEC ? i, CR,

"OUTPUT", CR,

SDEC ? i, SDEC ? drive, CR, CR



LOOP

Chris Savage

dbj,
·
·· Offset is not being declared as a variable or constant, which is why you’re getting that error.

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Chris Savage
Parallax Tech Support