What Is the Application Value of Thermocouple Signal Filter Modules for Hot Runner Systems?

The jump of thermocouple temperature signal is generally caused by electromagnetic interference generated by the injection molding servo motors, high-power heating coils and frequency converters, which affects the PID steady regulation and product molding quality. Thermocouple special signal filter modules are mounted between the sensor wire harness and temperature control cabinet to filter out clutter induced noise while not distorting effective thermoelectric potential signals, which is an economical and efficient anti-interference solution for hot runner production lines with severe electromagnetic noise. In this post we will talk about the idea of signal filter modules, their classification, how to wire them during installation and their practical production value.

The thermocouple signal filter modules are designed on the basis of dual-stage filtering of low frequency congestion and high frequency pulse interference. The first stage employs a passive RC low-frequency filtering circuit to suppress the low-frequency alternating magnetic field induced clutter caused by the servo motor operation, and smooth irregular small-range temperature jumps of 1-3℃. The second stage has high frequency magnetic ring absorption filtering, to filter out the instantaneous high frequency pulse noise generated when the inverter switches, to avoid sudden hyper high / low temperature false alert caused by immediate signal distortion. The internal circuit is designed for low impedance matching, suitable for the microvolt-level weak signals of thermocouples, without attenuating or delaying effective temperature feedback signals, unlike standard power filters which distort microvolt-level thermoelectric potential. The entire module is encapsulated with high temperature resistant PPS shell, may be put alongside the mold connection box near the hot runner, and to work stably for a long time under ambient temperature of 180℃ without circuit failure.

Three standard signal filter modules are classified to suit different hot runner wire schemes. The single channel independent filter module is appropriate for small molds with less than 8 temperature zones. Each thermocouple signal wire is fitted with an independent filter, which has the best filtering effect. It is straightforward to disassemble and replace the single channel when a single sensor fails. Multi-channel integrated filter junction box, integrate 16/32 groups of filter circuits into one sealed box, which is suitable for large multi-cavity hot runner molds with dense wiring harnesses, centralized wiring management, reduce scattered modules, save mold plate installation space. The plug-in quick-disconnect filter adapter is a tiny module that is mounted between the thermocouple plug and controller channel. No re-wiring the harness, plug and play, works well for production lines with frequent mold change-overs, easy to disassemble and move with the mold. The three kinds of modules have the same filtering performance, only difference in installation form and wiring ease, and can be selected according to the number of hot runner temperature zones and the mold change frequency.

Standard installation and wiring criteria to ensure maximum filtering effect. The shorter the length of unfiltered wire section from thermocouple to filter, the less clutter signal absorbed before filtering and the better the noise elimination effect. Install the filter module as close as feasible to the hot runner mold connection box. The filter thermocouple signal wires and heating power cables should be separated by more than 15cm and prevent laying in parallel over a long distance, and the vertical crossing arrangement can further decrease the secondary electromagnetic induction after filtering. The shielding braid of the thermocouple wire shall be grounded at one point of the grounding terminal of the filter module, and double-end grounding is prohibited to prevent the occurrence of ground loop current and the generation of new interference signals. Do not parallel several thermocouple signal lines to one filter channel. Each pair of positive and negative wires should have an own filtering circuit to prevent signal crosstalk across distinct temperature zones. For workshops with high humidity, please select the completely sealed waterproof filter module to avoid the short-circuit of internal circuit caused by condensed moisture.

Three primary aspects indicated practical production value: First, cut unplanned downtime and get rid of false warnings caused by temperature jumps. The electronic connector and new energy vehicle production lines are equipped with dense automation equipment, which originally generates dozens of temperature abnormal alarms every shift. After the installation of filter modules, the number of alarms has been reduced by more than 90%, and the machine runs continuously without frequent shutdown inspection. 2. Stabilize the curve of PID temperature control and decrease the defective product rate. After filtering out clutter noise, the temperature fluctuation amplitude of the hot runner zone is reduced from ±2-3℃ to within ±0.5℃. The flaws of gate wire drawing, haze and uneven dimensional tolerance of precision plastic parts are considerably improved, and the rejection rate can be lowered by more than 60%. Third, extend the service life of thermocouples and temperature controllers. Frequent signal clutter will cause frequent power switching of the controller power module, which accelerates aging; steady filtered signals minimize the switching frequency of heating coils, lower the loss of circuit modules, and avoid the burnout of the controller board caused by instantaneous pulse interference.

Selection ideas match diverse production contexts. Ordinary household appliance and package molds with low electromagnetic interference can employ low-cost plug-in quick-disconnect filter adapters. In the case of severe interference of electronic and automotive high-speed injection molding lines, use multi-channel integrated sealed filter junction boxes for centralized anti-interference processing. Medical cleanroom hot runner systems require medical grade low outgassing filter modules without volatile organic compounds in an effort to prevent pollution of cleanroom air and clear plastic items. Signal filter modules work with full-shielded thermocouple extension wires to constitute a whole anti-interference system. It has solved the electromagnetic noise signal distortion problems of hot runner thermocouples thoroughly.333