Abstract: Plastics have unique physicochemical properties. In the plastic production process, processing temperature is the key factor determining product quality. This paper discusses the specific application of Delta temperature controllers in the plastic processing production process to ensure precise control of raw material production temperature in complex production environments, avoiding high scrap rates caused by excessively high or low temperatures. Keywords: Temperature controller, molding system, plastic machinery 1 Introduction Plastic products are ubiquitous in production and daily life, and corresponding plastic production equipment is also diverse. Since the physicochemical properties of plastics are determined by the "three elements" in the processing process, namely "temperature, pressure, and time," it is difficult to achieve the desired physicochemical properties if these three parameters are not properly matched. Among them, temperature is the most important parameter. Therefore, most plastic product equipment cannot do without temperature controllers. The following uses a plastic extruder as an example to introduce the application of Delta temperature control. Plastic extruders are divided into single-screw and twin-screw types, mainly used for extruding soft and hard PVC, polyethylene and other thermoplastic plastics. With the corresponding auxiliary machines (including forming heads), they can process a variety of plastic products, such as films, pipes, rods, plates, filaments, tapes, cable insulation layers and hollow products. As shown in Figure 1, a plastic extruder uses multiple DTA temperature controllers to control heating, and each heater is equipped with a set of cooling fans or water cooling devices to regulate the temperature. Figures 2 and 3 show various Delta temperature controllers. [align=center] Figure 1 Plastic extruder Figure 2 Temperature controller (1) Figure 3 Temperature controller (2)[/align] 2 Temperature control in plastic processing is based on the characteristics of plastic raw materials. It is required that the controlled temperature cannot exceed the set temperature by ±2 degrees Celsius. If the temperature is too low, the material will not flow smoothly from the extruder, resulting in excessive load on the front extrusion mechanism; if the temperature is too high, it may change the characteristics of the raw materials and cause the work-in-process to be scrapped. On-site observations show that choosing the relatively easy-to-operate ON-OFF control method will cause significant oscillations, as shown in Figure 2. The controlled temperature will have an error of at least 3 degrees Celsius. Therefore, simple on/off control is not advisable. Generally, PID control is chosen. However, it's important to note that using the usual self-tuning method to obtain P, I, and D values ​​will actually cause even greater accuracy errors. This is because the DTA temperature controller does not support dual output functionality, so only single-output heating is possible. The cooling fan above the extruder is triggered by the DTA alarm output as a cooling output. DTA self-tuning requires natural cooling or a relatively constant cooling environment. Using an alarm for cooling control essentially turns it into a sudden event, exceeding normal conditions. This will shorten the cooling time and oscillation period. If the I value corresponds to (oscillation period/2), the I value will decrease, resulting in more severe oscillations. [align=center] Figure 4 Comparison of switch control and PID control[/align] During parameter tuning, the following should be noted: (1) Do not use self-tuning, manually input the P, I, and D values, because the three parameters P, I, and D have been adjusted to the default values ​​at the factory, P=47.6, I=260, D=41, which may result in a slower heating speed, but the control accuracy will also be relatively improved. As long as it is not in an environment with rapid temperature changes (100 degrees change in 5 seconds), the factory value can meet the control requirements. It is worth noting that the equipment can meet the requirements of the required working conditions with the factory setting value. On the contrary, performing self-tuning often results in incorrect parameters, causing temperature oscillations. If the temperature rise rate is accelerated, the P value should be appropriately reduced. (2) The cooling speed on plastic equipment is very slow, so when the temperature exceeds the limit, the alarm output is used to trigger the fan to accelerate cooling. Note that when using the alarm to drive the fan to cool in DTA, the ALARM range must be set to a large value (e.g., only when it exceeds 4 degrees). This is because the temperature is unlikely to exceed this range unless there is an abnormal situation. If the ALARM is set too small (e.g., 1 degree), exceeding the set value will cause the cooling speed to be too fast and will also cause temperature oscillation. 3 PID control and parameter adjustment The P value of the controller is actually the proportional control gain. The I value corresponds to the integral time (Ti), and the D value corresponds to the derivative time (Td). The P value refers to the proportional gain (as shown in Figure 4). If P is set to 20 and SV (target temperature) is set to 150 degrees, the output will be controlled in full output mode before 150-20=130 degrees. Therefore, if the P value is adjusted too small, the temperature will be overheated. The factory default value P is 47.6. To reach a temperature of 100 degrees Celsius, the proportional control output is applied at 100 - 47.6 = 52.4 degrees Celsius. Therefore, unless the heating speed is very fast, there will be no oscillation. According to the principle of automatic control, the controller output is a function of the P, I, and D parameters and the system error e, where e = PV (system output value) – SV (system setpoint). When the system output temperature equals the system setpoint temperature, the system error e is zero. At this time, there is no output in the P control. Without P output, it is impossible to maintain the temperature at the setpoint. In this case, integral I control is used to perform compensation. The I value refers to the integral quantity. Output = P quantity + I quantity + D quantity. However, when proportional control is not engaged, I control is not executed because the system is already in full output state, and the I quantity cannot be increased further. [align=center]Figure 5 Output Response of PID Control[/align] As shown in Figure 5, the integral action is triggered when the temperature first rises and then reverses to fall. At the start of heating, the temperature will already overshoot. If the integral amount is increased at this moment, the temperature will exceed the limit even more. Therefore, when the integral action is started, the smaller the Ti value, the larger the integral amount, and vice versa. Therefore, the factory default value of I is 260 to avoid the heating temperature being too high due to the large integral amount. [align=center]Figure 6 Response of Integral Regulation[/align] As shown in Figure 7, the I value is calculated from (cycle time/2). The temperature drop rate in the molding machine (without the fan running) is quite slow, so the I value will be quite large. However, the fan can be used to accelerate the cooling, which will greatly shorten the cycle time and the I value will become relatively much smaller, thus making the oscillation more severe. [align=center]Figure 7 Oscillation Caused by Integral Regulation[/align] The D value refers to the differential component. When the system temperature changes, D quantity control will be activated. In a heating system, if the temperature drops rapidly, the output (U) = P + I + D. Conversely, if the temperature rises rapidly, the output (U) = P + I - D. Therefore, D is used to control rapid temperature changes, enabling a quick response to reduce errors from the set value. A larger D value results in a faster response, and vice versa, as shown in Figure 8. If D is set too large, a rapid response to any temperature change may cause oscillations. If D is set extremely large, even a slight temperature change will cause a drastic change in the system output, potentially leading to divergence and loss of control. [align=center]Figure 8 System Response During Differential Adjustment[/align] 4 Conclusion The above briefly discussed the application of Delta temperature controllers in extruders. In summary, the following aspects are noteworthy during use: Using the alarm output in the DTA for cooling control and performing auto-tuning will result in incorrect PID values; in systems performing auto-tuning, it is recommended to tune the function first, and only manually adjust the PID parameters if the control effect is poor; the factory-set PID parameters are suitable for most systems, allowing for stable operation, but the time to reach the set value is slightly longer; OMRON control uses full output mode, and when the temperature exceeds the set value by 1-2 degrees, the fan starts rapidly to cool down, causing temperature oscillations and frequent fan starts, increasing energy consumption; in DTA's PID control, the temperature generally varies within the allowable range of the set value, and the fan hardly operates. During system operation, due to the flow of raw materials, the temperature can be controlled within a range of ±2-3 degrees. Because the DTB and DTC series offer dual output functionality, they can directly execute tuning functions or run with the factory-set PID values, achieving the same accuracy requirement of ±2 degrees.