The bench liquid cooling test for new energy vehicle components demands stringent accuracy in pressure measurement. Prolonged exposure to high and low temperature cycles, coupled with frequent pressure shocks, can readily cause instrument zero and span drift, necessitating regular standardized calibration. Here, we present a comprehensive calibration procedure, utilizing the Longlv PTL535 diaphragm-type digital pressure switch that can be directly executed on-site at the bench. This procedure is tailored for battery and motor electronic control water cooling test conditions.

1. Safety and tool preparation before calibration

    Shutdown and pressure relief: Shut down the rack liquid cooling circulation unit, completely drain the cooling liquid from the pipeline, confirm that the pipeline is at normal pressure with no residual pressure, and strictly avoid dismantling and calibrating equipment under pressure.

    Environmental tidying: Clear away the coolant and condensed water vapor around the instrument, wipe dry the diaphragm sensing end face, and avoid impurities affecting pressure transmission; check the diaphragm for any bumps or deformations. The diaphragm structure serves as the measurement benchmark, and any damage will directly lead to calibration failure.

    Supporting tools: Prepare a standard pressure calibration source, sealing adapter, and dust-free wiping cloth. Confirm that the accuracy level of the calibration equipment is higher than that of the instrument being tested to ensure the validity of the calibration results.

    Instrument inspection: Check whether the digital display screen of the machine body is flickering, whether the button operation is sensitive, and whether the sealed enclosure is free from condensation and water ingress.

II. Clean the diaphragm end face to eliminate the source of calibration error

PTL535 adopts a diaphragm isolation structure, where precipitates from the cooling liquid and trace impurities easily adhere to the surface of the isolation diaphragm, causing pressure transmission lag and calibration deviation.

Gently wipe the outside of the diaphragm with a dust-free soft cloth. Avoid scratching or applying excessive pressure to the diaphragm with hard objects. After cleaning, let it stand for a moment to ensure that the diaphragm is free of any attachments and has returned to its original shape due to the restoration of force. Then, connect it to the calibration equipment.

III. Atmospheric zero point calibration (basic step)

Fully depressurize the pipeline to standard atmospheric pressure, observe the reading on the PTL535 screen, and if the value is not zero, enter the settings menu through the function buttons on the device to perform zero calibration.

After calibration, maintain normal pressure for 3 to 5 minutes and repeatedly observe whether the readings stabilize and return to zero. If there is no drift or jump, it indicates that the zero point baseline calibration is complete. Under the working conditions of high and low temperature alternating tests on the bench, the probability of zero drift is higher. It is recommended to recheck the zero point before and after each test.

IV. Connect standard verification equipment for segmented pressure range calibration

    Connect the standard pressure source to the instrument pressure tapping interface through a sealing adapter, and confirm that there is no leakage at the connection.

    According to the commonly used pressure range for liquid cooling of new energy vehicle platforms, pressure is uniformly increased in multiple stages from low to high, covering three ranges: low-pressure standby, conventional test pressure, and peak impact pressure. After each stage of pressure increase, the system is allowed to stabilize before moving on to the next.

    Compare the values from the standard calibration device with the displayed values on the PTL535 screen. If there are deviations, use the panel buttons to fine-tune the range parameters to ensure consistency between the two sets of readings.

    Slowly increase and decrease the pressure throughout the entire process to avoid instantaneous high-pressure shocks that could damage the pressure-transmitting medium inside the diaphragm and compromise the measurement accuracy of the instrument.

V. Full-range cyclic retesting, adapting to bench alternating conditions

After completing zero point and single-point calibration of the measurement range, conduct multiple complete pressure rise and fall cycle tests, covering all pressure ranges of daily bench tests, and verify whether the numerical error in each pressure segment is within the allowable range.

Slowly release the pressure back to normal pressure, recheck whether the zero point has returned to zero, and if there is any deviation, repeat the zero point calibration process. If there is no significant error after multiple cycles, it indicates that the range calibration is qualified.

VI. Re-inspection of simulated bench low temperature environment (exclusive step for new energy vehicle bench)

The liquid cooling bench for new energy vehicles will undergo testing in sub-zero temperatures and high-low temperature cycles, which may cause slight temperature drift. After calibration, a brief simulation of a low temperature environment can be conducted, and the instrument readings can be observed while standing still. If the numerical fluctuations are small, it indicates that the temperature compensation performance is normal and meets the long-term testing requirements of the bench.

VII. Remove the calibration equipment and restore the bench test pipeline

    After slowly releasing the pressure, remove the standard pressure source and recheck that the diaphragm isolation membrane is intact and undamaged.

    Restore the connection of the liquid cooling pipeline and tighten the joints to prevent coolant leakage.

    Activate the bench circulation system, gradually increase the working pressure, and observe the digital display for stable and normal values. Once confirmed, proceed with the liquid cooling durability and performance testing of the components.

VIII. Precautions for using and calibrating the rack

    The diaphragm is a precision isolation component. During calibration and disassembly, squeezing and impact are strictly prohibited. If the diaphragm becomes dented, the instrument must be replaced;

    After the daily durability test of the test bench is completed, it is recommended to conduct a simple zero point recheck, and complete a full-range calibration once a week to ensure the accuracy of the test data;

    After replacing the coolant and cleaning the pipeline, recalibration is necessary, as residual medium can easily cause measurement deviation;

    After the instrument settings are completed, the parameter locking function can be enabled to prevent bench commissioning personnel from accidentally touching the buttons and changing the calibration parameters.