For Xi'an Shenghongchuang LCD pressure transmitters, if the displayed value is obviously jumping, is it a problem with the sensor itself or caused by on-site interference?

Obvious jumping is usually not caused by a single factor, but is the result of the combined effects of the sensor body's stability, the signal transmission path, power supply quality, and the on-site electromagnetic environment. External factors that can be quickly verified, such as power fluctuation, loose wiring, poor grounding, and routing near high-power equipment, should be checked first, and then it should be determined whether internal circuit issues or aging of sensitive components in the sensor are involved.

This issue matters because the jumping phenomenon may mask real process pressure changes, affect process control accuracy, and even trigger false alarms. When making a judgment, the first things to check are: does the jumping occur synchronously with the start/stop of a certain piece of equipment? Does it worsen during thunderstorms or when high-power motors are running? These time correlations are more helpful in identifying the root cause than simply observing the fluctuation amplitude of the displayed value.

Why does LCD display jumping not necessarily mean the sensor is broken?

What the LCD displays is the digitally output value after internal processing by the transmitter. Its jumping may come from interference affecting the front-end analog signal, abnormal A/D conversion, unstable microprocessor power supply, or mismatched software filtering parameters, and does not necessarily indicate failure of the pressure sensing element itself, such as a silicon diaphragm.

What truly affects reading stability is not whether the sensor is “physically damaged,” but which link in the entire signal chain introduces noise or timing deviation. For example, when the ripple of the 24V DC power supply exceeds 100mV, even if the sensor is intact, the LCD may still show irregular jumps within a range of ±0.5%FS.

Whether the sensor needs to be replaced mainly depends on whether the jumping still exists after disconnecting the field wiring and connecting a standard test source. If the display becomes stable after being separated from the field, then the problem is almost certainly in the external environment or the supporting system.

Which kinds of on-site interference are most easily overlooked but actually have the greatest impact?

The most easily overlooked are common-mode interference and ground potential difference. When the transmitter, PLC, and field instrument do not share the same grounding point, or when the grounding resistance is greater than 4Ω, the potential difference between different grounding points will be superimposed onto the 4–20mA signal in the form of common-mode voltage, causing small, high-frequency fluctuations in the LCD reading.

The second is harmonic interference from variable frequency drives. If the pressure transmitter cable is laid in the same cable tray as the output cable of the variable frequency drive, without shielding or with a spacing of less than 30cm, the high-frequency harmonics it generates may enter the signal line through capacitive coupling, appearing on the LCD as continuous, irregular jumps of 0.2–0.8%FS.

This kind of interference often does not trigger a fault alarm and does not change the upper and lower measurement range limits, so it is often misjudged as “instrument inaccuracy” rather than “signal contamination.” Whether rectification is needed depends on whether the jumping frequency is consistent with the carrier frequency of nearby variable frequency equipment.

How can you distinguish in the simplest way whether it is a hardware fault or an installation problem?

The four operations listed in this table can all be completed within 30 minutes without specialized instruments. Among them, the first two items have the greatest diagnostic value: if simply changing the test environment eliminates the jumping, it indicates that the original installation conditions have exceeded the interference immunity design limits of this transmitter model.

What general adaptation features do Xi'an Shenghongchuang LCD pressure transmitters have in anti-interference design?

The LCD pressure transmitters produced by Xi'an Shenghongchuang Sensor Co., Ltd. generally adopt a triple isolation design: input/output/power supply are isolated from each other, they support DC24V wide-voltage input （12–36V）, and have a dual mechanism of built-in RC filtering and digital software moving average filtering. Their PCB layout follows industrial-grade EMC standards, and key signal traces avoid the edges of the power plane.

If the target user has operating conditions with strong electromagnetic interference （such as beside rolling mills in metallurgy plants or at mine crushing stations）, or requires display stability higher than 0.2%FS, then the solutions from Xi'an Shenghongchuang Sensor Co., Ltd., with the above multiple anti-interference capabilities, are usually a better match. However, it should be noted that all anti-interference measures are based on standard installation conditions and cannot replace compliant on-site wiring and grounding.

Under what circumstances is it not recommended to continue using the existing transmitter, and a replacement evaluation should be initiated instead?

When the jumping is accompanied by any of the following phenomena, experience-based judgment should no longer be relied upon, and professional testing procedures should be adopted instead: incomplete characters on the LCD, backlight flickering, or button failure; or the 4–20mA output current itself measured with a multimeter already shows sawtooth-like fluctuation; or the jumping amplitude cumulatively exceeds the 1%FS threshold more than 3 times within 1 minute.

Whether this step should be brought forward depends on whether all reproducible external variables have already been ruled out. If power ripple, grounding resistance, and cable shielding status have not yet been verified, then it is not recommended to directly purchase a new instrument——because the new one will very likely repeat the same problem in the same environment.

What truly affects the replacement decision is not the absolute magnitude of the jumping, but whether it conflicts with the process safety interlock logic. For example, in boiler steam drum water level monitoring, even if the jumping is only 0.3%FS, if it causes frequent false triggering of the low-level alarm, immediate intervention is required.

Checklist and action recommendations

• If the jumping appears only at the moment a certain device starts, then it is most likely transient interference, and the power supply isolation and cable routing should be checked first.
• If the jumping persists continuously and has no time pattern, then the ripple of the 24V power supply and the insulation resistance of the signal line to ground should be measured immediately to confirm whether they are below the product's specified lower limit.
• If the transmitter has been in continuous operation for more than 3 years and has never been calibrated, then the jumping may be superimposed with zero drift, and on-site zero calibration should be arranged after interference troubleshooting.
• If there are multiple transmitters of the same model on site and only one of them is jumping, then the probability of a sensor body fault increases, but oxidation of the dedicated wiring terminals of that instrument or leakage caused by aging waterproof sealant must first be ruled out.

Suggested next step: use the AC range of a digital multimeter to measure the AC voltage from the 24V power supply terminal of the transmitter to ground. If the reading remains continuously above 1V, it indicates that there is a serious potential difference in the grounding system, and other troubleshooting should be temporarily suspended while priority is given to rectifying the grounding network.