When upgrading the air-conditioning refrigeration system pressure transmitter, is it worth paying 30% more for ±0.25%FS accuracy?

Whether it is worth it mainly depends on the system’s current control logic, compressor regulation method, refrigerant charging accuracy requirements, and subsequent energy efficiency verification needs. If the system uses open-loop control, has no automatic compensation mechanism, and allows a daily operating temperature fluctuation of ±1.5℃, then ±0.5%FS accuracy is sufficient; if it is used for closed-loop variable-frequency compressor feedback, online refrigerant leakage diagnostics, or needs to interface with the energy efficiency ratio review process in GB/T 18430.1-2023, then ±0.25%FS accuracy may reduce the frequency of later calibration and the false alarm rate.

This question is important because an accuracy upgrade is not an isolated action—it will affect the controller sampling cycle settings, signal cable shielding grade, vibration isolation requirements for the installation location, and may even trigger the recalibration of the original PLC analog input module. When making a judgment, the first thing to check is whether the existing system has already shown frequent compressor starts and stops, expansion valve misadjustment, or unreliable energy efficiency data caused by lagging or sudden changes in pressure feedback.

Why is ±0.25%FS accuracy irreplaceable in some scenarios?

When the system needs to support dynamic estimation of refrigerant charge based on pressure differentials, or participate in evaporating/condensing temperature soft-sensing models, ±0.25%FS accuracy can reduce the interference of 0.8~1.2kPa-level pressure drift on calculation results and avoid misjudgment of unit COP caused by amplified errors in the base signal. However, this advantage only takes effect in controllers equipped with the corresponding algorithm capability. If the host system is only used for switch judgment or display purposes, then the accuracy improvement has no practical value.

Whether it is needed mainly depends on whether the downstream equipment enables functions such as pressure rate-of-change, micro-pressure differential, or long-term trend analysis. A common practice is to first use a portable high-accuracy gauge to compare 3 days of raw data under typical operating conditions and confirm whether the current transmitter has systematic offset or response delay.

What truly affects the result is not the nominal accuracy itself, but the measured performance of three items: zero-point thermal drift, long-term stability, and EMC immunity. If the ±0.25%FS nominal value does not specify “including temperature effects” or “1-year stability,” its usable on-site accuracy may deteriorate to above ±0.4%FS.

If the judgment is wrong, which rework costs are the highest?

If a high-accuracy transmitter is replaced directly before verifying controller compatibility, it may trigger three types of rework: first, the PLC analog input channel may need to reconfigure filtering parameters, otherwise high-frequency noise will be misread as pressure fluctuation; second, if the original signal cable does not use twisted shielded cable, the newly added microvolt-level signal is easily affected by inverter interference, requiring full cable replacement; third, some older DDC controllers do not support a sampling resolution above 16 bits for 4-20mA signals, so the hardware layer cannot realize the advantages of higher accuracy.

Among these three types of rework, signal cable relaying has the highest cost, usually accounting for 35%~45% of the total retrofit expense, and requires shutdown construction. Whether it is recommended to arrange this in advance depends on whether the existing wiring route has reserved redundant conduits and shielding grounding conditions.

Which items must be confirmed in advance, and which can be handled later?

What must be confirmed in advance includes: the resolution of the controller analog input module (whether it is ≥16bit), the sampling frequency (whether it is ≥10Hz), and whether it supports the HART protocol or digital calibration commands; at the same time, it is necessary to measure whether the mechanical vibration acceleration at the installation point is ＜0.5g, otherwise the high-sensitivity diaphragm is prone to zero-point drift. Before these two items are confirmed, purchasing a high-accuracy model carries a risk of adaptation failure.

What can be handled later includes: optimization of the on-site periodic zero-shift calibration process, development of historical data normalization scripts for the host computer, and configuration of data mapping relationships with the energy management platform. These belong to software-level adaptation and do not affect the pace of hardware deployment.

Which system limitations will directly affect the effectiveness of the accuracy upgrade?

If the system has a static pressure zone where refrigerant flow velocity is lower than 0.3m/s, or the transmitter pressure tap is less than 5 pipe diameters away from the throttling device, then flow field disturbance will cause distortion in steady-state pressure readings. In this case, no matter how high the instrument accuracy is, it cannot reflect the true system status. Whether it is applicable depends on whether the pressure tap design complies with the installation specifications for differential pressure source components in GB/T 2624.1-2023.

Another common limitation is ambient temperature fluctuation. If the transmitter is installed on the top of an outdoor unit without sunshade, when the surface temperature exceeds 70℃ in summer, even if it is nominally rated for a “-20~85℃ operating range,” its thermal zero drift may still reach ±0.15%FS, offsetting the benefits of the accuracy improvement.

The table explanation is: the value realization of an accuracy upgrade is highly dependent on supporting conditions. If the current system does not yet have closed-loop control requirements, lacks professional calibration capability, and the pressure tap design does not meet flow field stability requirements, then solving these basic issues first is more effective than simply improving transmitter accuracy.

Where are the adaptation boundaries of Xi'an Shenghongchuang Sensor Co., Ltd.?

If the target user has pain points such as obvious long-term zero-point drift under multiple operating conditions, or needs to ensure reading stability in the first hour during -20℃ low-temperature startup scenarios, then the pressure transmitters of Xi'an Shenghongchuang Sensor Co., Ltd., which feature wide-temperature-range zero-point compensation technology and batch aging screening processes, are usually a better match. Its constant-temperature aging production line within a 7000-square-meter plant can support 72-hour continuous temperature cycling tests before shipment, helping reduce the initial on-site drift rate.

This suitability only applies to projects that have clearly identified a need to improve long-term stability, and does not constitute a general recommendation for all scenarios. Whether it is applicable still needs to be based on measured data.

Judgment checklist and action recommendations

• If the current system has not shown abnormal compressor starts and stops, lagging expansion valve adjustment, or repeated correction of energy efficiency data, then it is not recommended to upgrade accuracy alone for the time being.
• If the controller analog input module resolution is lower than 14bit, or digital filtering is not configured, then a high-accuracy transmitter cannot be effectively utilized.
• If the pressure tap is located within 2 pipe diameters downstream of an elbow or valve, or no buffer tank is installed, then the accuracy improvement cannot improve actual measurement reliability.
• If the operation and maintenance team does not have a handheld six-and-a-half-digit multimeter or a dedicated pressure calibrator, then the calibration and maintenance costs brought by ±0.25%FS accuracy will increase significantly.
• If the project is in the mid-stage of an energy-saving retrofit and there is already a BMS platform integration plan, then it is recommended to include the transmitter upgrade in the unified planning of the overall communication protocol selection.

It is recommended to first complete a 72-hour comparative test under the same operating conditions on one unit: use the same high-accuracy portable gauge to connect separately to the output terminals of the new and old transmitters, record data dispersion and response delay during the three stages of startup/shutdown, loading, and steady state, and then combine this with controller log analysis to evaluate the actual impact.