Today we'll look at the wiring of a temperature controller. It needs to collect the ambient temperature first, so a temperature sensor is required, usually a thermocouple or a resistance temperature detector (RTD). When the ambient temperature reaches the set temperature, it can automatically control the temperature, either raising or lowering it. Today we'll mainly discuss the most common feature: automatic power-off upon reaching the set temperature. Some temperature controllers also have upper and lower limits to maintain the ambient temperature within a certain range.
Temperature controller
The panel displays the temperature. P shows the measured temperature, which is the temperature transmitted by the temperature sensor , and S is the temperature we set.
Let's first get to know the temperature sensors we need.
A resistance temperature detector (RTD) is essentially a resistor, a type of metallic material that is sensitive to temperature changes. (I'm not sure what the specific material is, but it's unclear.) As temperature changes, the resistance changes, producing positive or negative values. It typically detects temperatures from 0 to 150 degrees Celsius, but can also detect temperatures below 0 degrees Celsius, classifying it as low-temperature detection. A thermocouple, on the other hand, is a bimetallic material. When temperature changes, a potential difference is created between the two metals. It detects temperatures from 0 to 1000 degrees Celsius or even higher, classifying it as high-temperature detection. RTDs come in 2-wire, 3-wire, and 4-wire versions. The output value is determined by the resistance change and the connecting wires. If the wires are too long, an extra few ohms of resistance can introduce significant temperature errors. Therefore, 3-wire or 4-wire systems are designed to eliminate these errors. If the wires are short and high temperature accuracy isn't required, a 2-wire system is sufficient.
Three-wire heating resistors are quite common.
Most thermocouples are two-wire, although three-wire ones also exist. Our temperature controllers generally only require two-wire connections.
1, 2 connected to thermocouple
For a three-wire heating resistor, connect it to 123.
The general control circuit is connected to an AC contactor.
An ALM (Automatic Leveling Module) is an auxiliary module, typically used to connect to alarm devices, usually an alarm or indicator light. It has a passive set of high and low output contacts, similar to relay contacts. It always has a common point; the low-to-high connection is normally closed, and the high-to-low connection is normally open. If the current temperature P reaches the set temperature S, the normally closed low-to-high connection opens, and the high-to-low connection closes.
Alarm indicator wiring
Automatic power off when temperature reaches the target level
If the operating voltage is 220V, connect the neutral wire to the live wire, and connect the ground wire if there is a ground symbol. Since the high/low positions are passive, a power line needs to be connected to the high position to form a control circuit with the contactor. The diagram above uses a normally closed contact, so the jumper can be connected to either the high or low position.
Delayed power outage
Sometimes we need to delay power off when a certain temperature is reached, which requires adding a time-delay relay. When the temperature is reached, the time-delay relay activates, the delay begins, and the power off automatically after the delay time is reached.
The wiring methods for different temperature controllers are largely similar; the connections for the temperature sensor , power supply, and relay output are all the same. If your temperature controller has an auxiliary module, please refer to the instruction manual.
