Section 12 — Instruments and Controls
Pressure and Differential Pressure Transmitters
IPE Engineering Practice IPE-EP-12-1-10
Document number: IPE-EP-12-1-10 · Section: 12 — Instruments and Controls
SCOPE
- Pressure and differential pressure transmitters shall be supplied in accordance with this Practice, the attached Data Sheet, and the referenced standards and publications.
- Where special features or improvements over the Practice are required as determined by the Owner, or Owner’s Engineer, these shall be specified on the Instrument Data Sheets and shall be adhered to by the vendor.
- Any deviation from this Practice must be approved by the procedure described in EP 1–1–3.
- A revision bar indicates all changes made to this Revision.
2.0 REFERENCES
The following codes and standards shall be considered as part of this Practice. All documents shall be the latest editions in force on the date of issuance of this Practice.
STANDARDS AND PUBLICATIONS
| IPE Engineering Practices |
|---|
| EP 1–1–3 Deviations to IPE Engineering Practices EP 12–1–1 Control Systems EP 12–1–2 Supplemental Requirements for Control Systems EP 12–1–10 DS Pressure and Differential Pressure Transmitters Data Sheet EP 12–1–19 Pressure Gauges |
| ASME |
| B 1.20.1 Pipe Threads General Purpose (Inch) |
| ISA Standard |
| S 50.1 Compatibility of Analog Signals for Electronic Industrial Process Instruments |
| NEMA |
| ICS 6 Enclosures for Industrial Controls and Systems |
| NFPA |
| 70 National Electrical Code |
DEFINITIONS
- Inspector - A Inflection Point Engineering, LLC. appointed engineer or inspector.
- Manufacturer - The recipient of a direct or indirect purchase order for materials and/or equipment. In this context, a direct order is one issued to a manufacturer by a contractor or the Owner. An indirect order is one issued to a manufacturer by a vendor (recipient of a direct order) for materials, fabricated components, or subassemblies.
- Owner - Inflection Point Engineering, LLC .
- Owner’s Engineer - A Inflection Point Engineering, LLC . appointed engineer.
DESIGN AND MATERIALS
- The transmitter shall consist of a pressure or differential pressure sensor providing an output signal proportional to the input to the sensor.
- Pressure and differential pressure sensing elements and body shall be Type 316 stainless steel as a minimum. Other alloys may be substituted by the manufacturer with the approval of the Owner’s Engineer. The manufacturer shall notify the purchaser of the suitability of various metallurgy and material for the specified service.
- Pressure and differential pressure transmitters shall have a minimum static pressure rating of 1500 psig for the pressure containing boundary.
- Pressure, including absolute pressure, transmitters shall be designed for an over-range pressure of the greater of 100 psig or 150% of the maximum sensor range without affecting the calibration of the instrument. Differential pressure transmitters shall be designed for differential pressure over-range, in either direction, of the body pressure rating without affecting the calibration of the instrument. Transmitters in vacuum service shall be designed to withstand full vacuum without shifting calibration more than 1/2 of 1% of the range.
- Transmitter sensing element temperature limits shall be at least -40 o F to +220oF.
- Threaded connections shall be tapered and shall conform to ASME B1.20.1
- Air supply and output connections for pneumatic transmitters shall be internally threaded 1/4 inch NPT.
- Electrical transmitters conduit connections shall be internally threaded 1/2 inch NPT.
- When specified, the transmitters shall be furnished with a, stainless steel, three way manifold valve assembly. Other alloys may be substituted with the approval of the Owner’s Engineer.
- Transmitters shall be furnished with a vent/drain valve. The valve shall be of the same material or better as the transmitter body (or flanges), and shall be separate connections. The vent should be located near the top of the instrument and the drain should be near located in the bottom.
INSTRUMENT AND MOUNTINGS
- Electronic transmitters shall be listed by Factory Mutual (FM) or Underwriters Laboratory (UL) for the National Electric Code area classification Class 1, Groups B, C, and D Division 1. In addition, housings shall be weatherproof NEMA type 4. Pneumatic transmitters shall be weather proof NEMA type 3.
- All transmitters shall be suitable for universal mounting on either yoke or surface type installation, as specified on the Data Sheet.
- Yoke mounted instruments shall be furnished with a device for attachment to an un-threaded end of a 2” pipe.
CALIBRATION
- Conventional transmitters shall be shop calibrated for a transmitted signal range which shall correspond linearly to the differential pressure or pressure range specified on the Data Sheet. The calibrated span should be in the upper one half of the capsule range. Calibrations in inches of water shall be interpreted as inches of water at 68oF for flow transmitter.
- Intelligent transmitters shall be calibrated to the manufacturers normal values and re-ranged to the differential pressure or pressure range specified on the Data Sheet, unless the specified zero and span warrants an additional bench calibration.
ELECTRONIC TRANSMITTERS
- Transmitters shall be the two wire type providing an isolated 4 to 20 mA signal, in analog mode, while operating from a remote power supply of nominal 24 V DC (actual 23 to 32.7 V). The detailed requirements are type 2U in ISA S50.1. Intelligent transmitters shall be capable of operating in a analog and digital mode.
- Intelligent (smart) transmitters shall be capable of being remotely configured, re-ranged, and diagnosed by a handset communicator through the signal wiring. Intelligent transmitters, operating in digital mode shall be capable of driving two remote indicators.
- Transmitters shall be adjustable span, adjustable zero types. Span shall be adjustable from one sixth to full capsule range. Zero shall be adjustable plus or minus 50% of the capsule range.
- Single component failures shall not permit process fluids to enter the transmitter conduit and shall meet the requirements of NEC Article 501-5(f)(3) without additional seals.
- Transmitters shall have screw terminations for field wiring connections. Terminals shall be marked for polarity, test connections, etc., and shall be in a enclosure suitable for the electrical area classification.
- Transmitter zero adjustment shall be accessible without exposing electronics and shall not affect span calibration.
- Transmitters shall be provided with adjustable damping.
- Differential pressure transmitters for level measurement shall be managed so that increases in level shall increase the output. Reverse acting transmitters shall not be used. If required, transmitters shall be supplied with additional zero suppression capabilities so that zero output can be obtained with the specified value of suppression.
- Local electronic indicator, when specified on the Data Sheet shall meet the electrical classification of the transmitter.
PNEUMATIC TRANSMITTERS
- Transmitters shall be force balanced type providing a output signal of 3 to 15 psig while operating from a filtered and regulated 20 psig air supply.
- Transmitters shall be adjustable span type. Span shall be adjustable from one quarter to full capsule range. Zero shall be adjustable plus or minus ten percent of capsule range. Access to the zero adjustment shall be provided without removing the instrument case.
- Differential pressure transmitters for level measurement shall be arranged so that increases in level shall increase the output. Reverse acting transmitters shall not be used. If required, transmitters shall be supplied with additional zero suppression capabilities so that zero (3 psig) output can be obtained with the specified value of suppression.
- A combination air reducing valve and filter set complete with a bracket for surface mounting shall be furnished for each pneumatic transmitter. Air sets for use with instruments not equipped with air supply pressure gauges shall be furnished with internal pressure gauges to indicate the reduced air pressure. air sets shall be designed for operation on an air supply of 40 to 100 psig.
- Local indicators, when specified on the instrument data sheets, shall be furnished by the manufacturer. Receiver gauges shall conform to EP 12-1-19.
PERFORMANCE
- Each transmitter shall be capable of meeting the performance requirements when the installation, operation, maintenance, and adjustment of the equipment has been in accordance with the manufacturer’s submitted instruction, and the equipment has not been subjected to over-range pressure greater than that listed in section 4.4.
- Overall accuracy (express as % of Data Sheet specified span), including the combined effects of linearity, hysteresis, and repeatability, shall be equal to or better than:
| Pneumatic | Electronic | Intelligent |
|---|---|---|
| 0.5% | 0.2% | 0.1% |
- The error due to static pressure effects for conventional electronic transmitters shall not exceed:
| zero | 0.5%/1000 psi of upper range limit |
|---|---|
| span | 0.5%/1000 psi of upper range limit |
The error due to static pressure effects for intelligent transmitters shall not exceed:
| zero | 0.1%/1000 psi of upper range limit |
|---|---|
| span | 0.25%/1000 psi of upper range limit |
- The error due to power supply effect shall not exceed:
| conventional | 0.01% of calibrated span/volt |
|---|---|
| intelligent | 0.005% of calibrated span/volt |
- A 100oF ambient temperature change between the range of 0 to 175oF shall not result in calibration effects greater than the following limits for conventional electronic transmitters.
Zero error: 3.0% of minimum span 0.5% of maximum span
Total effect: 3.5% of minimum span 1.0% of maximum span (including span and zero errors)
A 50oF ambient temperature change between the range of 0 to 175oF shall not result in calibration effects greater than the following limits for intelligent transmitters.
Total effect: 0.50% of maximum span (including span and zero errors)
- Radio frequency and electromagnetic interference with a field strength of 30 volts/meter or less, over a frequency range of 20 MHz through 1000 MHz, shall not result in an additional transmitter output error greater than of 0.1% of the upper range limit of the capsule.
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