The technical requirement communication checklist for custom pressure transmitters should include 8 core parameters: measurement range, medium characteristics, installation method, output signal, accuracy class, protection rating, power supply requirements, and ambient temperature range; if the medium corrosiveness, overload capacity, explosion-proof rating, or electrical interface type are not clearly defined in advance, it can easily lead to prototype rework or inability to install on site.

Such customized products do not have the fault-tolerance margin of standard models, and there is strong coupling among technical parameters. For example, choosing the wrong process connection thread can make it impossible to connect to the existing pipeline, misjudging the chemical composition of the medium may cause diaphragm corrosion failure, and ignoring the level of on-site electromagnetic interference can result in 4–20mA signal drift. Whether rework is required mainly depends on whether the missing parameters affect structural implementation or the baseline of safety compliance.

Why must the measurement range and overpressure capacity be confirmed first?

The measurement range directly determines the range design of the sensor core sensitive element, while the overpressure capacity (such as 1.5 times or 2 times full scale) relates to diaphragm thickness and material selection. Together, these two parameters determine the elastic body structure scheme, and once finalized, they cannot be corrected later through circuit adjustment.

If only the normal operating pressure is provided but possible water hammer, pulsation, or shutoff shock is not specified, permanent diaphragm deformation is likely to occur during actual operation. Whether a high-overpressure design is required depends on whether there are transient pressure mutation scenarios in the process system.

A common practice is to require the customer to provide the maximum expected pressure value and its frequency of occurrence, rather than only marking the “usual operating pressure”. For positions such as pump outlets and compressor buffer tanks, it is recommended to back-calculate the overpressure margin based on the system safety valve opening pressure.

Which unclear medium characteristic parameters are most likely to cause rework?

The medium name alone is not sufficient to support selection; specific information such as temperature, viscosity, solids content, PH value, oxidizing/reducing properties, and whether it contains hydrofluoric acid or chloride ions must also be provided. For example, if it is labeled as “wastewater” but contains a high concentration of sodium hypochlorite, a standard 316L stainless steel diaphragm will suffer pitting perforation within half a year.

Whether special materials are needed depends on the actual corrosion rate of the medium on wetted parts, rather than purely on industry convention. In chemical projects, Xi'an Shenghongchuang Sensor Co., Ltd. often matches solutions such as Hastelloy C276 and tantalum diaphragms based on the MSDS or third-party corrosion reports provided by customers.

What truly affects the outcome is not “whether it is corrosive”, but “whether corrosion occurs in stress concentration areas such as the sealing surface, pressure port, or diaphragm edge”. This judgment requires cross-verification combining fluid dynamics simulation and material electrochemical data.

Why can’t the installation method and process connection be left until the drawing stage to decide?

The installation method (such as flange type, threaded type, or sanitary clamp type) determines the structural dimensions of the transmitter body, the form of the pressure-bearing housing, and the routing of the internal pressure-guiding channel. Different connections correspond to completely different machining molds and assembly tooling, and the cost of switching is far higher than rewriting a circuit board.

If the goal is to replace existing equipment, the original manufacturer's connection standard number (such as ANSI B16.5 Class 150, DIN 11851) and flange sealing face type (RF/RTJ) must be provided. If it is only described as “using M20×1.5 male thread” without specifying whether it is metric fine thread or imperial NPT, it will result in inability to tighten on site.

Whether this step should be moved forward depends on whether piping construction drawings or equipment layout drawings already exist. If there are no drawings, priority should be given to collecting photos of the actual object and measured data with a vernier caliper, rather than relying on verbal descriptions.

What hidden dependencies exist between the output signal and power supply requirements?

4–20mA two-wire is the most commonly used solution, but if intrinsic safety requirements exist on site, the associated safety barrier model and the upper limit of loop impedance must be confirmed simultaneously; if RS485 digital output is selected, the Modbus RTU protocol version, baud rate, and parity mode must be specified.

The power supply voltage range (such as 12–36VDC) seems simple, but it actually affects the internal constant current source design and temperature compensation algorithm. Wide-voltage input requires an additional DC-DC isolation module, which changes the PCB layout and the heat dissipation structure of the enclosure.

Whether HART protocol overlay is required depends on whether the host system supports a HART handheld communicator or DCS card. If this point is not confirmed before production, remote configuration and diagnostic functions will be completely unavailable.

The table shows that structural and safety parameters must be frozen before the technical agreement is signed, while some electrical performance parameters can be set by programming before shipment. Whether production can proceed depends primarily on whether the first five items have formed a closed-loop confirmation record.

Which technical parameters can still be negotiated and adjusted after the contract is signed?

Zero offset, range scaling ratio, damping time constant, LCD backlight on/off logic, and similar items are software-configurable and usually do not involve hardware changes. As long as the main control chip resources allow it and the original design margin is not exceeded, all can be set during the factory inspection stage.

However, note: if the offset exceeds ±20% of the original range, it may affect the linearity specification; if the damping time is set above 10 seconds, the dynamic response capability will be significantly reduced. Although these adjustments do not require rework, they will affect fulfillment of the performance commitment.

Whether later adjustment is recommended depends on whether the user has already grasped the actual fluctuation characteristics of the operating conditions. It is recommended to collect a 72-hour pressure curve after the initial commissioning, and then decide whether to optimize the filtering parameters.

Judgment Checklist and Action Recommendations

• If complete physical property data of the process medium (including temperature, corrosive components, and particle size) have not yet been obtained, then it is not recommended to start the customization process, otherwise there is a fundamental risk of misjudgment in diaphragm material and sealing scheme.
• If the on-site installation space has not been actually measured (especially when there are hard constraints on flange spacing, instrument height, and junction box orientation), then even if all other parameters are clear, it may still be impossible to install in place due to structural interference.
• If the control system has not yet determined the communication protocol type (such as Modbus ASCII/RTU/ASCII) and terminal resistor configuration method, then there is a protocol incompatibility risk for digital-output transmitters, and it is recommended to postpone ordering.
• If the project is in the early design stage and the piping discipline drawings are not yet finalized, then a flexible adaptation solution should be reserved for the process connection size (such as a dual-thread adapter), to avoid binding to a single standard.
• If the budget allows and the delivery schedule is flexible, then one functional prototype can be produced first for on-site operating condition verification, and then replicated in batches, greatly reducing the probability of system-level adaptation failure.

It is recommended to immediately prepare a 12-field "Pressure Transmitter Customization Requirement Confirmation Form", to be jointly signed by the process, equipment, and instrumentation parties and attached to the technical agreement, ensuring that all strongly coupled parameters form a written closed loop.