PLC Voltage Regulation or Control?

MaxHeadRoom

Joined Jul 18, 2013
28,619
One, the items were all the same size so the power level and on time was fairly predictable, if your application is similar I am not sure how you are going to get or even need variable control from feedback.
Is there any reason that the same programmable time duration and settings cannot just be repeated, if it is a question of reducing power after initial heating then a simple non feedback control could be implemented, what is the nature of the material? does it vary all that much?
Max.
 

Thread Starter

HighVoltage!

Joined Apr 28, 2014
181
One, the items were all the same size so the power level and on time was fairly predictable, if your application is similar I am not sure how you are going to get or even need variable control from feedback.
Is there any reason that the same programmable time duration and settings cannot just be repeated, if it is a question of reducing power after initial heating then a simple non feedback control could be implemented, what is the nature of the material? does it vary all that much?
Max.
They can vary in mass or length. Usually long cylindrical rods.
 

strantor

Joined Oct 3, 2010
6,782
So the Phase angle fired SCR will be wired directly to line voltage replacing variac (control), the PID receives the temperature signal, lets say once PID decides a raise in temperature is needed, a signal is put out (4-20mA output signal) indicating ON in which I assume will be the ANALOG INPUT of the PAF SCR. How is this controlling (Raising/lowering) the voltage when its just putting out an ON/OFF signal? Meaning you somehow must pre-set your desired voltage = your desired output current? Can it handle up to 100A? Also, for initial start-up, the temperature is going to be close to ambient meaning the PAF SCR will start high at max voltage to try and get temperature quicker onto "load" (can limits be set lets say for "Max Voltage" = safety?...If not, I believe its unnecessary to stress equipment/wiring). Does the PAF SCR learn like the PID's autotune mode?
The phase angle fired SCR accepts an analog input from 4mA to 20mA, with 4mA corresponding to 0% output voltage, and 20mA corresponding to 100% output voltage. The signal is linear between those points, so for example 12mA would be 50%.
Let's say the signal is 12mA (50%); the SCR will output a half-sine wave as shown in this picture:

That's equivalent to 240VRMS if full sine is 480V.

Now, the PID analog output PID controller does not output a digital ON/OFF signal. It outputs an analog signal between 4mA and 20mA. Let's say you first turn it on, and everything is cold; it's going to put out 20mA (100%) and the SCR is going to pass the full 480V. As temp starts to come up, the PID controller will gradually lower its output signal in an analog fashion, down from 20mA to 19mA, 18.5mA, 18mA, ... and so on, until it gets to whatever power output level keeps the temp in a steady state.

Read the link I posted; yes it can handle 100a
 

Thread Starter

HighVoltage!

Joined Apr 28, 2014
181
The phase angle fired SCR accepts an analog input from 4mA to 20mA, with 4mA corresponding to 0% output voltage, and 20mA corresponding to 100% output voltage. The signal is linear between those points, so for example 12mA would be 50%.
Let's say the signal is 12mA (50%); the SCR will output a half-sine wave as shown in this picture:

That's equivalent to 240VRMS if full sine is 480V.

Now, the PID analog output PID controller does not output a digital ON/OFF signal. It outputs an analog signal between 4mA and 20mA. Let's say you first turn it on, and everything is cold; it's going to put out 20mA (100%) and the SCR is going to pass the full 480V. As temp starts to come up, the PID controller will gradually lower its output signal in an analog fashion, down from 20mA to 19mA, 18.5mA, 18mA, ... and so on, until it gets to whatever power output level keeps the temp in a steady state.

Read the link I posted; yes it can handle 100a
Interesting and simple enough since I already have a pid all I need is the scr. Can a voltage max output set-point be set for scr?
 

Thread Starter

HighVoltage!

Joined Apr 28, 2014
181
The phase angle fired SCR accepts an analog input from 4mA to 20mA, with 4mA corresponding to 0% output voltage, and 20mA corresponding to 100% output voltage. The signal is linear between those points, so for example 12mA would be 50%.
Let's say the signal is 12mA (50%); the SCR will output a half-sine wave as shown in this picture:

That's equivalent to 240VRMS if full sine is 480V.

Now, the PID analog output PID controller does not output a digital ON/OFF signal. It outputs an analog signal between 4mA and 20mA. Let's say you first turn it on, and everything is cold; it's going to put out 20mA (100%) and the SCR is going to pass the full 480V. As temp starts to come up, the PID controller will gradually lower its output signal in an analog fashion, down from 20mA to 19mA, 18.5mA, 18mA, ... and so on, until it gets to whatever power output level keeps the temp in a steady state.

Read the link I posted; yes it can handle 100a

Will this do? https://www.watlow.com/products/controllers/power-series-solid-state-controls.cfm

It already has the PID controller in the unit itself!
 

dannyf

Joined Sep 13, 2015
2,197
It already has the PID controller in the unit itself!
Unless you are dealing with large thermal loss or low thermal mass, PID introduces no benefits.

I would go with simple on/off controls instead.
 

strantor

Joined Oct 3, 2010
6,782
Will this do? https://www.watlow.com/products/controllers/power-series-solid-state-controls.cfm

It already has the PID controller in the unit itself!
I'm familiar with those; used to have them in IR heaters in the wire & cable plant. They were controlled by a PLC, and i didn't remember anything about onboard PID. I didn't see anything on the product page about onboard PID so I skimmed the datasheet and still didn't see anything about it.

If you're sure they have it, then I won't argue with you, but I offer the friendly suggestion that you check again.

If you want PID and SCR in one package, check out Spang Power Products. They have a feature called "direct temperature control" which I believe implies PID although it isn't expressly stated. I've seen their digital controllers used in heating applications with no external controller.
 

Thread Starter

HighVoltage!

Joined Apr 28, 2014
181
I'm familiar with those; used to have them in IR heaters in the wire & cable plant. They were controlled by a PLC, and i didn't remember anything about onboard PID. I didn't see anything on the product page about onboard PID so I skimmed the datasheet and still didn't see anything about it.

If you're sure they have it, then I won't argue with you, but I offer the friendly suggestion that you check again.

If you want PID and SCR in one package, check out Spang Power Products. They have a feature called "direct temperature control" which I believe implies PID although it isn't expressly stated. I've seen their digital controllers used in heating applications with no external controller.
Your right there wasnt a pid controller built in...I was looking at chromolax website as well which was the link I meant to copy/paste...woops. I will check them out!
 
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