Digital Thermostats

On/Off or PID Control

Digital thermostats are the best way of controlling temperature as they offer accuracy and reliability. They clearly show the actual temperature and will open and close the circuit depending on the type of control method selected.

CONTROL TYPE

on/off or PID control

INPUT TYPE

Thermocouple or RTD

OUTPUT TYPE

Relay or SSR

POWER SUPPLY

85-250v or 12/24v

TEMPERATURE CONTROL METHODS

ON/OFF CONTROL

This is the most commonly used type of control where a temperature is set and once it has been achieved opens the control circuit. This is used on very basic controls such as mechanical thermostats or digital temperature controllers. These should be used where the temperature accuracy is not critical and over-shooting is not a major problem. Typically suited for temperatures under 200 deg C

PID CONTROL

This option should be chosen when temperatures are required to stay within a very short band width. Over-shooting or low turn “back on temperatures” would cause a product to be damaged or scrapped would be costly. These types of controllers will ensure this does not happen.

PROCESS CONTROLLERS

These types of controllers do the same as PID controllers with the added feature of being able to set “Ramp/Dwell” times also. This would be typically useful in a process where the temperature is required to get to a given set point and then hold for an predefined time before ether rising or lowering again. They also have feature that allow them to communicate with other main process systems.

TEMPERATURE SENSORS

We offer two types which are commonly used over 90% of applications, they are thermocouples and RTD(PT100). Thermocouples are generally suitable for a wide range of temperatures and should be chosen for the majority of applications Type K has a range up to 1000 deg C and type J up to 700 deg C.

RTD(PT100) sensors are more accurate and will control within 1/10th of a deg C depending on the controller. The temperature is more linear so with be more accurate over a larger temperature span.

FAQs

proportional–integral–derivative controller (PID controller)

This is called a feedback control loop which continuously measures the value between the actual and required value set-point. This then applies a correction value based on PID (Proportional, Integral and Derivative).

What this means is that it automatically corrects any detected errors and over-shooting and continuously checks against the set point.

If this is the case, usually its down to the sensor bulb location. Check that it is positioned correct where the heat source is. Ideally they should be inserted into the object being heated.

If you seen 3 or 4 dashed lines on the display, this normally means that the sensor cable is lose or is broken. Replace this for continued use.

If you need accuracy within 1 deg C/F or less then the use of PT100 input is better as they usually controller with 1/10th of a C/F depending on controller. They are also linier so are more accurate over a wide temperature range. Otherwisethe use of Thermocouples should be used.

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