Power Matching and Temperature Control for 26mm Cartridge Heaters

An injection moulding machine does a work that needs the mould to be 250°C. The operator sets the controller to 250°C, but the temperature actually changes between 240°C and 260°C. Parts come out with different sizes. People criticise the heating system, however the underlying problem could be that the wattage of the 26mm large diameter single head electric heating tube doesn't meet the tuning of the controller. To keep the temperature stable, you need to use the right power and control technique.


The first thing to think about is picking the right wattage for the job. If you don't provide the 26mm single head electric heating tube enough power, it will take too long to achieve the setpoint. The heater will keep going over the target temperature if you give it too much electricity. This will cause thermal cycling, which shortens the life of the heater and puts stress on the mould. A good rule of thumb is to make the heater so that it runs at around 60–80% of its maximum duty cycle when it is in steady-state operation. This gives you room to warm up at first without the severe cycling that happens with heaters that are too big.

To figure out how many watts you need, you need to know the mass of the object you want to heat, the temperature rise you want, and the heat losses from the system. Convection losses can be large for a mould with a lot of surface area that is open to the air. A single-head electric heating tube with a 26mm diameter that is put in a big mould may need to produce twice the wattage that was anticipated based on mass and specific heat alone in order to make up for continuous losses. Calculating heat loss should also take into consideration cooling channels, ejector pins, and other parts that act as heat sinks.

After choosing the wattage, the way you control it becomes very important. On-off control (sometimes termed bang-bang control) turns the cartridge heater all the way on until the temperature reaches the setpoint, and then all the way off until the temperature drops below a hysteresis band. For a single head electric heating tube with a 26mm diameter, on-off control works well for applications with a wide temperature range, like ±5°C. On-off control can generate temperature swings that can damage product quality when tighter tolerances are needed.

Proportional-integral-derivative (PID) control makes things run more smoothly. Instead of turning off the cartridge heater completely, a PID controller lowers the power to it as the setpoint gets closer. This proportionate power delivery keeps the 26mm single head electric heating tube constantly powered at a lower level, which keeps the temperature consistent without cycling. PID control makes heaters last longer because the parts inside don't have to go through frequent thermal expansion and contraction. A lot of current controllers have auto-tuning functions that automatically measure the system's temperature response and figure out the best PID parameters.

Thyristor power controllers (also known as silicon-controlled rectifiers or SCRs) can fire in phase angle or burst mode for applications that need the most accuracy. By cutting the AC waveform, phase-angle firing changes the power that the cartridge heater gets. This technology gives you almost unlimited control resolution, but it also makes electrical noise. Burst firing cycles turn on and off entire half-cycles, which makes less noise but lowers the resolution a little. For regulating a 26mm big diameter single head electric heating tube, both approaches work much better than mechanical relays.

Another thing that influences how well the control works is where the sensors are placed. The thermocouple or RTD that measures the mould temperature should be as close to the cartridge heater as feasible without being in the path of the heat. If the sensor is too far away from the heater, it will take longer to respond, which will make the controller go too far. A sensor that is too close may read temperatures that are too high because of heat radiation from the heater sheath. Putting the temperature sensor halfway between two 26mm cartridge heaters and at the same depth as the heaters gives the most accurate measurement.

The power wiring also has to be looked at. A single head electric heating tube with a 26mm diameter and 2000 watts at 240 volts carries roughly 8.3 amperes. The wires that connect the controller to the heater must be able to handle at least this amount of current, plus some extra protection. Wires that are too small cause voltage drop, which means that less power is actually sent to the cartridge heater. This difference between the controller output and the heater input makes the temperature unstable, which is very annoying. To get consistent and reproducible results in every thermal management problem, from simple platen heating to sophisticated multi-zone systems, you need to carefully combine heater power, controller calibration, and sensor location.