Testing the CMRR of a hot runner system requires injecting a controllable common-mode signal and measuring the output deviation. The CMRR is then calculated using a formula. This test is typically performed in a laboratory or high-precision maintenance environment to ensure the temperature control system can operate stably even under electromagnetic interference.
1. On-site Testing Procedure (Requires Professional Equipment)
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Steps |
Operating Instructions |
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Prepare Signal Source and Measuring Tools |
Use an adjustable AC power supply (simulating common-mode interference), a high-precision digital multimeter or oscilloscope, and a standard thermocouple simulator |
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Establish Test Loop |
Connect the thermocouple input to the temperature controller. Apply a 50Hz/60Hz AC voltage (e.g., 10Vrms) to the neutral point of the signal line as common-mode interference. |
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Inject Common-Mode Signal |
Apply an AC voltage of the same amplitude (simulating ground loop noise) simultaneously to the positive and negative terminals of the thermocouple. |
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Measure Output Fluctuation |
Record the maximum temperature deviation displayed on the temperature controller and convert it to an equivalent millivolt error (ΔmV). |
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Calculate CMRR |
Calculate the CMRR value based on the input common-mode voltage and output error. |
Example: Applying a 10V common-mode voltage, the temperature controller shows a temperature drift corresponding to a 1.4mV error (≈40℃), then CMRR ≈ 80dB.
3. Alternative On-Site Assessment Methods (No Dedicated Equipment Required)
If laboratory facilities are unavailable, CMRR performance can be indirectly assessed through the following methods:
Observe temperature stability: During the start-up and shutdown of a high-power motor, check for jumps or spikes in the hot runner temperature control.
Use an oscilloscope to test the signal: Connect an oscilloscope probe in parallel with the thermocouple wire and observe for the presence of high-frequency noise superposition.
Compare shielding effectiveness: Enable/disable grounding of the shielding wire and observe whether temperature fluctuations are significantly improved.
Replace with a high CMRR module for testing: Temporarily connect a temperature control module with a CMRR ≥ 100dB and compare the degree of improvement in system stability.
Recommendation: For high-requirement industries such as automotive and medical, formal CMRR testing and certification should be commissioned periodically by a third-party organization.
4. Supporting Measures to Enhance Testing Effectiveness
Calibrate sensors and instruments before testing to ensure basic accuracy;
Test under typical operating conditions (such as full load operation) to more closely simulate real interference environments;
Record multi-channel data and analyze the consistency of response across each hot runner;
Verify overall temperature control performance using TUS testing.
Safety Principle: "Professional testing + on-site verification + regular evaluation"-the combination of these three ensures the reliable anti-interference capability of the hot runner system.
