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Hi, I’m not at all sure that this is the correct category, but here goes.
I’m a physics grad student, and I’m looking for a PID temperature controller. The system outline is simple enough: I have a sample stage with cylindrical holes that fit a heater resistor and a thermocouple, and I need a controller to heat up the stage using the resistor up to a setpoint temperature.
At the moment, what we have is a “dumb” setup where the heater is connected to a simple current source that we turn on and off manually when the thermocouple reads the correct temperature, however, we want an off-the-shelf solution so that we can park at a set temperature.
We will only ever need to go as high as 160 C, and the output power we have now (and does the trick well) is ~20W. Can anyone recommend a DigiKey product that can fulfill these requirements?
This is a common application. Low-cost controllers are available such as the ones shown on this DigiKey page. Chances are high you already have a similar controller built into the bottom of a laboratory grade oven or hot plate.
We can help you select an appropriate controller if you provide additional information about your project including:
source voltage for the resistive heater
resistance of the heater
sensor type
need for data to be sent to a PC
In addition, it would be helpful to describe the thermal mass of the system and the importance of fine temperature regulation. For example, if the material is relatively bulky and the temperature tolerance is not critical, we may be able to use a simple on off control. If this is a critical application, we may need to locate a Pulse Width Modulation (PWM) for DC or phase control for an AC application.
Thanks for the quick reply.
At the moment, the system is built in a slightly unorthodox way. We have 72V of voltage on a ~300Ohm heater, so the current is 0.26A. As I understand (by talking to more experienced people), this high-voltage-low-current setup is atypical.
The sensor is a pretty regular temperature sensor using a J-type thermocouple. There is no need for data to be read to a computer, and it’s much more important the the temperature remain precise than accurate, i.e. if I set it to 140 and it stabilized on 142 plus-minus 0.1, I’ll be overjoyed.
About thermal mass: it’s difficult to say at the moment, but it seems that the power we get from the current setup of ~20W is good for us, so a controller that can hold the appropriate voltage and current for that will work well. We are, of course, open to swapping the heater for something else, because I was told that ours has a higher resistance than is usually used for this kind of application.
Filtering PID temperature controllers for J type thermo coupler and control method PID we have a variety of options available for consideration. Linked here
May be filtered further by desired supply voltage and physical dimensions.
If we view this from a system level, it would be much easier and safer to construct a 24 VDC system. Both the heater and the PID controller could be powered from a single benchtop power supply thereby eliminating the mains wiring.
A resistive heater with a 25 Ω or 30 Ω resistance could be used. We could then drive the heater using a solid-state relay for long life.
Perhaps you could send pictures of your device that would help us converge on a solution.
Before I continue, I just want to point out that I’m a total novice in this technical stuff, so a few phrases you used went over my head, but I believe I get the gist.
In principle yes, we can change the heater, as long as we can then encase it with the same case used for the current one. The casing is important because it’s used to slide it into the sample stage that it heats.
I’m attaching some photos.
Based on your setup, I see two possible solutions:
Industrial control using a PID controller
Leverage the capabilities of your B&K Precision Model 1787B power supply.
PID controller
As pointed out by @Kristof_2649, we do have several PID modules. For example, the first device in the list should work for your system.
For long life, recommend you couple the PID controller with a use a solid-state relay. Note that 72 VDC is not within the window for DC solid state relays. You may need to change the heater.
Control the B&K Precison power supply
Your B&K Precision power supply likely has a DB09 serial interface. This allows remote control with a high degree of control, just like when you operate the power supply manually. You could wrap this power supply into a PID control loop using an Arduino and an interface such as this
Note that this module is for K type thermocouple.
Know that the Arduino has a tremendous code bas and active and helpful community. It will take some time, but I believe you will be able to stitch together a solution. You may be able to recruit assistance in your facility as the Arduino is popular with education.
Parting thoughts
I trust this note has given you some things to think about. Either way, you have some system design issues to consider as the parts must work together as a system.
IMHO, controlling the power supply is the preferred solution as the power supply will provide a smooth continuous control of the heater while the PID control module is an on off device. This is especially important if you want a steady temperature with no thermal cycling.
