The primary criteria for determining whether a hot runner system possesses adequate grounding performance are: verifying that the AC voltage-to-ground is below 1V AC, confirming that the ground resistance is ≤ 4Ω, and ensuring that the system utilizes a single-point grounding scheme. If multiple grounding points exist or if the ground potential difference is excessive, ground loop interference can easily occur; this disrupts thermocouple signals and triggers erratic fluctuations in temperature readings.
Three Key Standards for Assessing Good Grounding Performance:
1. AC Voltage-to-Ground ≤ 1V AC (Critical On-Site Criterion)
Use a multimeter set to the AC voltage range to measure the voltage between the negative terminal of the thermocouple and the earth ground.
If the voltage is < 0.1V AC: The grounding status is ideal, with no significant ground potential difference.
If the voltage is > 1V AC: A significant risk of ground loops exists, which is highly likely to cause temperature readings to jump erratically.
It is recommended to perform this measurement while the equipment is in operation to capture the actual potential difference under real-world working conditions.
2. Ground Resistance ≤ 4Ω (Fundamental Safety Standard)
Use a ground resistance tester (such as a 3-wire method tester or a clamp-on ground resistance meter) to perform the measurement.
The standard value should be ≤ 4Ω; this serves as the universal safety threshold for low-voltage electrical systems.
If the measured resistance is elevated (e.g., > 10Ω), it indicates poor contact at the ground electrode, corrosion, or insufficient burial depth, requiring immediate corrective action.
3. Implementation of Single-Point Grounding (System Architecture Requirement)
All temperature control modules, manifold housing enclosures, and shielding layers should be connected to a single, common, low-impedance grounding point.
Avoid sharing a common ground electrode with high-power equipment-such as injection molding machines or hydraulic stations-to prevent the introduction of external interference sources.
Multiple grounding points can easily create circulating currents due to ground potential differences and are a common root cause of erratic temperature readings.
Practical Tip: You can combine a "cold-state test" (performed while the system is shut down and de-energized) to verify connection reliability, and then measure the AC voltage while the system is running to make a comprehensive assessment of the grounding system's overall health.
