Yes, the VH is the model number and he uses a different brand of PID. The reason the fan needs to be slower is to prevent temperature overshoots and to stop the cooking chamber getting full of ash. The fan blows 16CFM and probably only needs to be half that. The Control Output mode is set to PID and the Output Mode is set to Time Duty.
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And can you get the speed to change as you heat up the thermocouple? Or, can you set the parameters to a value that forces the fan to a slower speed at ambient? What you are trying to demonstrate at this point is that the PID controller is controlling the motor with pulses. You might also be able to prove this using the multimeter on AC setting - the pulses will look like an AC voltage to the multimeter, and so the reading should change as the thermocouple heats up and the pulses change.
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Can’t go past an oscilloscope in this situation.
Looking at the attached “spec” (???) for what it is worth it looks like the model ITT-100V outputs DC 12V, 30mA. If this output is PWM (I doubt it) it will need to drive a low side Mosfet switch to control motor speed. If it is just an ON / OFF pulse it would need to drive a switch as above or a relay, which it is apparently doing with the SSR (usually require 3-30V input.
Lance will not be able to drive the blower directly from this output (30mA).
Lance can you post the exact make and model number. What you have posted doesn’t say much. There has got to be more info somewhere.
The pic of the rear of the unit tells nothing also. Don’t see what the connections are.
Lance forget about the “pot”. The correct term used in this configuration would be rheostat or variable resistor anyway. Allowing for the fact that Wattage rating refers to the whole of the resistive element you would have to allow 10 or more watts rating I think to be safe. A very rare pot indeed. You should be able to find a wire wound rheostat or some large variable resistor (the ones with a slider clamp for adjustment) but they are expensive.
Cheers Bob
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The 100R is clearly designated as a 'device for driving a relay. It is most likely that the output of the 100V is a pulse train. It is described as ‘Voltage Pulses Output’ at 12v, the diagram indicates it should be connected to a SSR with no mention of a requirement for a resistive load, and the options for the Output Mode are ‘Time Duty’ (probably duty cycle) or 0-10mA (variable current drive). A PID device that does not implement speed control in some form has little advantage over a simple on/off control with some hysterisis, and if the 100V was not a PID with speed control then there would be little point in having two different models (or modes - whichever it is). The real question is whether the device is configured correctly to output a pulse train, and whether the form of that pulse train is suitable for controlling the motor. A CRO would be an easy way to test that, but it is apparent that OP has access to nothing more complex than a multimeter, which might adequate for resolving that first part of the question.
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Hi All.
Just a thought. All of the temperature controls, PID or simply ON/OFF, I have had dealings with have always controlled the one or more heating elements NOT the fan or fan speed. Are we sure this control is being used as intended. We are only going on what some guy in the UK supposedly did to convert a BBQ into a smokehouse. His reference to a potentiometer in series to control fan speed is a bit sus for a start.
I have had some dealings with this sort of thing a few years ago at Mittagong where a small factory had a couple of large ovens with 45kW heaters to bake off the varnish on transformers, ballasts and other inductive components. These were ON?OFF systems with a hysteresis of about 10ºC which in 200º is not too bad. They did have a PID system at another point on another product line.
Cheers Bob
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Hey Bob and all,
In terms of controlling the temperature you are going to have a much much faster transient using a convective method - fan or exhaust system. The temperature differences will be very high and displacing the air can lead to some odd measurements.
Controlling the heating element with a known output into a closed/passively mixed volume will yield much more consistent results.
The PI part of the control will definitely be suited for this application but leaving the derivative term in might cause some overshoot, burning the food.
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Hi All
I want to thank you all for your input but it has got to the stage where I’m suffering from information overload. At this point all I’d like to know is: If I run the PID with a 12VDC power supply, can I run the fan straight from the SSR.
Cheers
Lance
Hi Lance
Unless we have a terminology mix up you are running the fan via the SSR now. If you mean “can I run the fan straight from the PID” device the answer I think is NO.
Cheers Bob
Hi Bob
What I’m asking is if I run the PID with 12VDC, do I take away the AC/DC adapter and run the fan straight off the SSR? In other words: 12VDC power supply to PID to SSR to fan?
Cheers
Lance
You still need the 12v Adapter, but you can drive both the fan and the PID from 12v, That avoids having open 240V connections, and is strongly recommended.
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Thanks Jeff, will give that a go.
Cheers
Hi Lance
Jeff has got it. The connections from PID to SSR only switch the SSR on and off. You still have to provide fan power (AC/DC adaptor) through the SSR.
Cheers Bob
Hi Bob
I Googled rheostat and this popped up. I realise it’s called a pot and you said to stay away from them but I’m wondering if it would be suitable?
Cheers
Lance
https://www.jaycar.com.au/5-ohm-15-watt-linear-b-wire-wound-potentiometer/p/RP3975
Hi Lance
Should be. It can dissipate 15W over the whole length of the resistive element and you could be using most of it so that should be ok.
Incidentally Element 14 call these rheostats. I suppose in theory it could be both. If the requirement was to use all 3 connections in a voltage divider configuration then you might call it a potentiometer. If (as you would) only use the centre and 1 outer connection so it would actually be a variable resistor it would be called a rheostat. As the latter would be the most used scenario for this device in my time it would be called rheostat.
Cheers Bob
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Hi Bob
Thanks for that, I’ll give it a try.
Cheers
Lance
