Corpus sync: neutrality remakes, note hygiene, datasheet relocation, transformer-split cross-refs
---
title: Process Instrumentation
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# Environmental and Service Conditions {toc}
−## Instruments shall be selected and rated for the ambient and process conditions at the installation point. {note}
+## Instruments shall be selected and rated for the ambient and process conditions at the installation point.
## The process variable, range, and location for each instrument are [[drawing: as indicated on the P&IDs and the instrument index]]. {note}
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### Digital fieldbus (FOUNDATION Fieldbus H1 or PROFIBUS PA per IEC 61158) multidrops multiple instruments on one pair with both power and data, reducing wiring on large multi-instrument installations, but requires fieldbus-capable I/O and segment engineering. {note}
+### Transmitters shall provide the selected output, and 4-20 mA instruments shall be two-wire (loop-powered) unless the measurement principle requires four-wire power.
+
```datasheet
label: Signal / Output Type
…8 unchanged lines
```
−### Transmitters shall provide the selected output, and 4-20 mA instruments shall be two-wire (loop-powered) unless the measurement principle requires four-wire power.
−
### The output type shall be coordinated with the control-system I/O type and the loop power supply under [[sync/control-systems-integration]].
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### A differential-pressure (DP) transmitter measures the difference between two connections and is the workhorse for DP-based level, filter and strainer differential, and pump differential — and for DP flow, which is covered separately in [[sync/flow-measurement]]. {note}
+### The pressure transmitter shall measure the selected type of pressure for the service.
+
```datasheet
label: Pressure Measurement Type
…7 unchanged lines
```
−### The pressure transmitter shall measure the selected type of pressure for the service.
−
## Calibrated Range {toc}
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### A diaphragm seal (remote or direct) isolates the transmitter from the process where the medium is corrosive, viscous, slurry-laden, fouling, or at a temperature that would damage the transmitter. {note}
+### Where the process fluid is incompatible with direct connection, the transmitter shall be furnished with a diaphragm (chemical) seal of materials compatible with the process.
+
```datasheet
label: Pressure Process Isolation
…7 unchanged lines
```
−### Where the process fluid is incompatible with direct connection, the transmitter shall be furnished with a diaphragm (chemical) seal of materials compatible with the process.
−
## Pressure Wetted Materials {toc}
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## Level Measurement Technology {toc}
−### Level technology shall be selected for the medium, the vessel, and the process conditions. {note}
−### Hydrostatic (submersible or DP) level infers level from the head pressure of the liquid column; it is simple and inexpensive, well suited to open tanks, wet wells, and clarifiers, but reads true level only at a known, constant specific gravity. {note}
−### Non-contact radar measures the time of flight of a microwave pulse to the surface; it is unaffected by density, vapor, and temperature, tolerates agitation and coating better than ultrasonic, and is the default for new closed-vessel and many open-channel applications. {note}
−### Guided-wave radar (TDR) sends the pulse along a probe, giving a strong, focused echo for low-dielectric, turbulent, or foaming media and for interface measurement, at the cost of a process-wetted probe. {note}
−### Ultrasonic measures time of flight of a sound pulse through the vapor space; it is non-contact and economical for open tanks and channels but is degraded by heavy vapor, foam, temperature gradients, and turbulence. {note}
−### Float and displacer devices give simple, reliable point or continuous level on clean liquids and are common for sump and tank switching. {note}
+### Level technology shall be selected for the medium, the vessel, and the process conditions.
```datasheet
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default: "Non-contact radar (microwave TOF) — default continuous"
```
+### Hydrostatic (submersible or DP) level infers level from the head pressure of the liquid column; it is simple and inexpensive, well suited to open tanks, wet wells, and clarifiers, but reads true level only at a known, constant specific gravity. {note}
+### Non-contact radar measures the time of flight of a microwave pulse to the surface; it is unaffected by density, vapor, and temperature, tolerates agitation and coating better than ultrasonic, and is the default for new closed-vessel and many open-channel applications. {note}
+### Guided-wave radar (TDR) sends the pulse along a probe, giving a strong, focused echo for low-dielectric, turbulent, or foaming media and for interface measurement, at the cost of a process-wetted probe. {note}
+### Ultrasonic measures time of flight of a sound pulse through the vapor space; it is non-contact and economical for open tanks and channels but is degraded by heavy vapor, foam, temperature gradients, and turbulence. {note}
+### Float and displacer devices give simple, reliable point or continuous level on clean liquids and are common for sump and tank switching. {note}
### The level instrument shall employ the selected measurement technology for the service.
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### The measured level range shall be [[drawing: as indicated on the tank/vessel data and the instrument index]] and shall include the dead band (blocking distance) at the top of the range for radar and ultrasonic instruments.
−### Radar and ultrasonic instruments have a near-field blocking distance below the sensor in which they cannot measure; the usable measuring range must account for it so the high-level set point does not fall in the blind zone. {note}
+### Radar and ultrasonic instruments have a near-field blocking distance below the sensor in which they cannot measure; the usable measuring range must account for it so the high-level set point does not fall in the blind zone.
## Hydrostatic Specific-Gravity Basis {toc}
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### Choose an RTD for accuracy and stability at moderate temperature, and a thermocouple where the temperature exceeds the RTD range or rugged high-temperature service is required. {note}
+### The temperature element shall be the selected sensor type for the service.
+
```datasheet
label: Temperature Sensor Type
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```
−### The temperature element shall be the selected sensor type for the service.
−
### RTDs shall be wired three-wire as a minimum to compensate for lead resistance, and four-wire where the specified accuracy requires it.
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### A thermowell that fails the wake-frequency check can resonate and fracture at the root under flow-induced vibration, dropping the broken tip into the process and opening a leak path; the ASME PTC 19.3 calculation is a mandatory check, not a formality. {note}
+### The thermowell type, insertion length, and material shall match the process connection, line size, and medium [[drawing: as indicated on the instrument index and piping details]].
+
```datasheet
label: Thermowell Type
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```
−### The thermowell type, insertion length, and material shall match the process connection, line size, and medium [[drawing: as indicated on the instrument index and piping details]].
−
## Temperature Transmitter {toc}
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### The spare-parts list with manufacturer part numbers shall be included in the closeout documentation.