Here we shall see detailed specifications of Transmitters used for Level, Pressure, Flow, DP applications.
The transmitter used for flow, pressure, level, and DP applications are generally digital foundation Fieldbus type (depends on plant and budget).
For shutdown/interlock systems transmitters should have the following features.
- Transmitters should be SMART type
- 2 wire 4-20 milliampere signal to be used
- Should support HART protocol
Generally, transmitters shall be
- Certified Exi
- Die-cast Aluminium body
- 2” yoke mounted
The material of the transmitters shall be normally SS 316, as a minimum. And should withstand 1.5 times the maximum pressure.
A capacitive type sensor should be used. Inductive sensors are not allowed.
Transmitters shall be provided with external zero adjustment and internal vent/drain provision.
The display should be LCD with an engineering module.
The transmitter should be microprocessor-based and it shall have non-volatile memory that can store configuration.
Signal conversion should be carried out in transmitter itself and the design of the electronics should be in compliance with Electromagnetic Compatibility requirements as per IEC 60801.
It should run a complete diagnostic routine and in the event of a failure, it should be driven to the predefined value of output.
Built-in temperature sensors shall be provided for temperature compensation wherever required.
Transmitter rangeability shall be 100:1. The transmitter shall be able to assure the accuracy of +/- 0.1% of the span for a rangeability of 1:10 unless otherwise specified in the job specification. The accuracy shall include the combined effect of linearity, hysteresis, and repeatability. The effect of static pressure on the transmitter in either direction shall be negligible.
The transmitter should have a calibrated range within the turndown ratio of 1:10. Normal-pressure shall never be more than 75% of calibrated range in steady conditions and shall never be more than 60% in fluctuating services.
The response time of the transmitter shall be less than or equal to half of the scan time of the control system.
Transmitter shall support the latest version of the HART protocol. It shall also support multiple masters at the same time as the central control system as a primary master and secondary master would be a handheld communicator or diagnostic computer.
Generally, the transmitter used in anti-surge control loops shall be non-smart type and flameproof unless specified otherwise.
Retrofit transmitters are not allowed.
Process connection for standard pressure & differential pressure transmitter shall be ½” NPTF and flanged for diaphragm seal type. Diaphragm seal element with capillary shall be used for congealing, corrosive, and highly viscous services at high operating temperatures. Capillary shall be of minimum SS 316, shall have SS 304 armoring with PVC cover, and with ID selected to have minimal lag. Flushing rings shall be provided with screwed vent & drain connections duly plugged.
Transmitter shall be installed with 2/3/5 valve manifold according to necessity.
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Author: Kalpit Patel
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