To ensure the accuracy of insulation resistance testing for hot runner systems, the key lies in the following: controlling environmental temperature and humidity; using the megohmmeter (500V DC) in accordance with proper protocols; adhering to standard operating procedures (such as performing "cold-state" tests and ensuring adequate discharge); conducting segmented measurements to pinpoint fault locations; and regularly calibrating testing equipment to prevent interference from factors such as surface contamination, residual charges, and induced voltages.
1. Control Key Environmental Factors
Temperature Stability:
Insulation resistance values decrease as temperature rises. It is recommended to perform "cold-state" testing at room temperature (20–25°C) to avoid the influence of high temperatures-present immediately after shutdown-on the readings. If "hot-state" testing is unavoidable, the temperature must be recorded and converted to a standard reference value to allow for comparison with historical data.
Humidity Control:
When the relative humidity of the air exceeds 70%, a conductive water film can easily form on insulation surfaces, resulting in falsely low measurement readings. Before testing, ensure that the mold is dry; in humid environments, use a dehumidifier or a heat gun (set to ≤80°C) to pre-dry the connector areas.
Clean the Work Surfaces:
Wipe down connector terminals, heating element housings, and cable plugs with anhydrous alcohol to remove oil stains, mold release agent residues, and carbonized deposits, thereby preventing surface leakage currents from affecting the overall resistance value.
2. Select and Calibrate Testing Equipment Correctly
Select the Appropriate Megohmmeter:
Use a digital megohmmeter with an output voltage of 500V DC and a measurement range covering 0 to 10 GΩ. A maximum output current of ≥1 mA is recommended to enhance the device's resistance to interference.
Utilize the Guard Terminal (G Terminal):
In high-humidity or contaminated environments, connecting a guard wire to the G terminal can effectively eliminate the influence of surface leakage currents on the measurement results, thereby improving accuracy.
Calibrate Instruments Regularly:
Calibrate the megohmmeter according to the manufacturer's recommended schedule (typically every 6 to 12 months) to ensure that measurement errors remain within permissible limits and to prevent misdiagnosis caused by equipment drift.
3. Standardizing Testing Procedures
Power Off and Fully Discharge:
Before and after every test, the system under test must be discharged to ground for a duration of no less than 1.5 times the charging time (a minimum of 5 minutes is recommended). This prevents residual charges from causing falsely elevated readings or damaging the test instrument.
Segmented and Isolated Measurement:
Avoid testing the entire system in parallel, as this may mask single-point faults. Instead, disconnect each circuit individually and measure the insulation resistance to ground for the cable harness, connectors, and heating element body separately to precisely pinpoint the source of the problem.
Readings at a Fixed Pressurization Time:
In accordance with established protocols, record the megohmmeter reading exactly one minute after applying voltage. At this point, the polarization process has largely stabilized, making the results more consistent and comparable.
4. Eliminating External Interference
Avoid Induced Voltage:
When conducting measurements in the vicinity of energized equipment, induced voltages may be present, posing a safety risk and interfering with readings. Use shielded cables, ensure proper grounding, and-if necessary-install temporary shielding devices.
Ensure Good Contact:
Poor contact between the test probes and the measurement points can introduce contact resistance, thereby compromising the accuracy of the results. Clean the terminals and firmly press the probes into place to ensure a reliable connection.
