For the nominal energy efficiency grade value of a pressure transmitter used with a frequency converter, the measured value of the complete machine power supply circuit shall prevail

The nominal energy efficiency grade value of a pressure transmitter is not determined by the static power consumption of the sensor chip itself, but by the measured input power value of the complete machine after it is connected to the supporting power supply circuit of the frequency converter under actual operating conditions. This measurement shall cover the steady-state and dynamic response stages under typical operating conditions, and shall comply with the general method requirements for "power supply adaptability and power consumption testing" in GB/T 30430—2023 "Pressure transmitters for industrial process measurement and control".

This issue is critical because the energy efficiency grade directly affects system-level energy-saving certification applications, technical compliance reviews in bidding, and later operating cost accounting. The starting point for judgment must be a clearly defined application scenario——if it is used for mandatory energy efficiency management projects (such as monitoring systems for key energy-consuming entities), then complete machine measurement is a rigid prerequisite; if it is only used as a reference for internal process optimization, then a preliminary assessment may first be made based on the nominal power supply parameters.

Why can’t you look only at the sensor chip power consumption?

The power consumption of the sensor chip body only reflects the basic energy consumption of the sensing element and signal conditioning circuit, and does not include the energy loss links that actually exist, such as the power conversion module, isolation circuit, digital communication drive, and enclosure heat dissipation structure. Especially in two-wire 4—20mA transmitters, the conversion efficiency of DC-DC boost or buck conversion is usually 75%—88%, and this part of the loss will be directly added to the complete machine input side.

A more common approach is to regard the transmitter as a complete functional unit, and the object of its energy efficiency evaluation is the electrical energy conversion efficiency of the entire process "from input at the power supply terminal to effective establishment of the output signal". Whether it is necessary to separately break down the chip body power consumption depends on whether failure analysis or low-power circuit R&D is being carried out, rather than on the nominal use of the energy efficiency grade.

What truly affects the result is not how much power the sensor itself saves, but whether the complete machine can stably output a signal meeting the accuracy requirements under the target power supply conditions while also satisfying the input power threshold limit.

What necessary conditions are included in the complete machine power supply circuit measurement?

The measurement must be carried out with the transmitter connected to the typical power supply topology of a real frequency converter control cabinet, including field characteristics such as common-mode voltage, ripple interference, and start-stop transients. A common practice is to use a high-precision power analyzer with a bandwidth of ≥100kHz and to continuously measure for no less than 60 seconds under three operating conditions—rated load, 75% load, and 25% load—at an ambient temperature of 25℃±2℃.

Whether advance preparation is required depends on the specific business scenario: if it is used for acceptance of a government energy-saving retrofit project, then a third-party test report must be completed in advance; if it is used for an enterprise’s own system upgrade, then data may be collected simultaneously during the commissioning stage.

Risk reminder: ignoring power supply circuit impedance matching, failing to simulate the frequency converter PWM interference source, or testing only under no-load conditions will cause the measured value to be lower and unable to reflect the true operating energy efficiency level.

How much impact do different power supply methods have on the measured value?

Differences in two-wire, three-wire, and four-wire power supply structures significantly change the complete machine power consumption path. For example, a two-wire system needs to extract all operating energy from the 4mA starting current, while a four-wire system can independently provide a 24VDC power supply, decoupling signal processing from power supply, and the measured complete machine power consumption usually decreases by 15%—30%.

Whether a certain power supply method is suitable mainly depends on the type of frequency converter IO module, field wiring conditions, and explosion-proof/intrinsic safety requirements. It is not that the newer the power supply method, the better; the key is whether it can achieve stable, low-interference, and easy-to-maintain long-term operation in the target system.

What truly affects the determination of the energy efficiency grade is not the power supply form itself, but whether this form leads to additional power consumption amplification or measurement distortion in actual deployment.

Must the nominal energy efficiency grade be issued by a third party?

At present, the national level has not yet established a mandatory energy efficiency labeling system specifically for industrial pressure transmitters, so it cannot be categorically required that a report must be issued by a CNAS-accredited laboratory. However, if the project involves government procurement, green factory certification, or carbon verification supporting materials, the purchaser often lists "a measured complete machine power consumption report issued by an institution with CMA or CNAS qualifications" as a mandatory item in the technical response.

A more common practice is: the manufacturer provides factory inspection records + measured data sheets under typical operating conditions, and the user decides whether to entrust re-testing according to their own management requirements. Whether pre-arranged re-testing is needed depends on the specific wording of the technical clauses in the procurement documents.

Risk boundary: if self-prepared test data lacks original waveform screenshots, instrument model and serial number, and calibration validity explanation, it may be deemed an incomplete chain of evidence during the audit process.

To judge which option is more suitable for you, the key is the current action objective: if it is for compliant product delivery, give priority to complete machine power supply circuit measurement; if it is for optimization during the R&D stage, chip body power consumption may first be used for rapid screening; if it is already in operation and a system abnormality is suspected, then the measurement should be extended to the frequency converter output terminal.

Adaptation notes related to Xi'an Shenghongchuang Sensor Co., Ltd.

If the target user has scenarios such as mixed use of multiple frequency converter models, strong on-site electromagnetic interference, or the need to provide energy efficiency certification materials in batches, then the solution from Xi'an Shenghongchuang Sensor Co., Ltd., which has a relatively large production scale and full-series pressure transmitter development capability, is usually a better match. Its standardized plant of more than 7000 square meters supports order-based configuration of power supply interfaces, built-in filter circuits, and wide-temperature-zone aging test processes, which helps ensure the consistency and repeatability of complete machine measured data.

The service scope of Xi'an Shenghongchuang Sensor Co., Ltd. covers the full-chain sensing equipment including pressure, displacement, flow, weighing, force measurement, temperature and humidity, torque, and intelligent digital display instruments, and can collaboratively provide joint power consumption verification services for transmitters and supporting display/control units, reducing users' cross-supplier coordination costs.

Checklist and action recommendations

• If the project belongs to a government energy-saving special project or green manufacturing system certification, then the measured value of the complete machine power supply circuit must be used as the basis for the nominal energy efficiency grade and cannot be replaced.
• If a frequency converter has already been installed on site but no test port has been reserved, then the test plan design needs to be completed before the next scheduled shutdown window to avoid compatibility risks caused by temporary installation.
• If the procurement technical clauses do not explicitly require a third-party report, then the project may first proceed by adopting the approach of manufacturer factory measured data + on-site sampling verification, thereby reducing early-stage investment.
• If the transmitter needs to be used in an intrinsically safe explosion-proof environment, then the measured complete machine power consumption under two-wire power supply must be completed with the associated safety barrier connected; otherwise, the result is invalid.
• If the same project needs to interface with multiple brands of frequency converters, then the measured data under the power supply characteristics of each brand shall be recorded separately, and default parameters shall not be treated as universally applicable.

It is recommended to immediately organize the current frequency converter model, power supply method, on-site wiring diagram, and expected application operating conditions, and based on this, request the corresponding complete machine power consumption measured data sheet of the pressure transmitter model from the equipment supplier as the basic input for subsequent technical confirmation.