Instrument Design for Process Equipment

NeqSim includes an instrument design framework that mirrors the existing electrical design and mechanical design systems. After running a process simulation, the instrument design system automatically determines which field instruments are required for each equipment item, generates ISA-5.1 tag numbers, classifies safety instruments by SIL level, counts I/O channels, and estimates instrument and control system costs.

Architecture Overview

The instrument design follows the same composition pattern as ElectricalDesign and MechanicalDesign:

ProcessEquipmentInterface
  └── getInstrumentDesign() ──► InstrumentDesign (base)
                                    ├── InstrumentList
                                    │     └── InstrumentSpecification (per instrument)
                                    └── InstrumentDesignResponse (JSON)

Equipment-specific subclasses add the correct instruments for each equipment type:

Equipment Instrument Design Class Key Instruments
Separator SeparatorInstrumentDesign PT×2, PSH, TT, LT×2, LSH, LSLL, ZT×2
Compressor CompressorInstrumentDesign PT (suction/discharge), PDT, PSHH, TT (suction/discharge/bearings), TSHH, FT, FCV, VT×4, VSHH, ST, lube oil PT/PSLL
Heat Exchanger HeatExchangerInstrumentDesign TT (in/out), PT (in/out), PDT, TSHH; type-specific additions
Pipeline PipelineInstrumentDesign PT×2, TT×2, FT, ZS×2 (pig), PSHH, PSLL
Valve ValveInstrumentDesign ZT, ZC; safety valves add XV, ZSO, ZSC
System (plant-wide) SystemInstrumentDesign Aggregates all equipment; sizes DCS/SIS cabinets

Quick Start

// 1. Run process simulation
ProcessSystem process = new ProcessSystem();
Stream feed = new Stream("feed", gas);
feed.setFlowRate(50000.0, "kg/hr");
Separator sep = new Separator("HP Sep", feed);
Compressor comp = new Compressor("1st Stage", sep.getGasOutStream());
comp.setOutletPressure(50.0);
process.add(feed);
process.add(sep);
process.add(comp);
process.run();

// 2. Get individual equipment instrument design
InstrumentDesign sepInstr = sep.getInstrumentDesign();
sepInstr.calcDesign();
System.out.println("Separator I/O: " + sepInstr.getTotalIOCount());
System.out.println("Separator cost: " + sepInstr.getEstimatedCostUSD() + " USD");
System.out.println(sepInstr.toJson());

// 3. Get plant-wide instrument summary
SystemInstrumentDesign sysInstr = process.getSystemInstrumentDesign();
sysInstr.calcDesign();
System.out.println(sysInstr.toJson());

1. InstrumentSpecification (ISA-5.1)

Each instrument is represented as an InstrumentSpecification — a data sheet entry following ISA-5.1 / ISA-20 conventions.

Analog Instruments

For transmitters and continuous measurements (PT, TT, LT, FT, VT, ST):

InstrumentSpecification pt = new InstrumentSpecification(
    "PT",           // ISA-5.1 symbol
    "Inlet Pressure",  // service description
    0.0,            // range minimum
    100.0,          // range maximum
    "bara",         // engineering unit
    "AI"            // I/O type
);

Discrete / Safety Instruments

For switches and trip devices (PSH, LSLL, TSHH, VSHH, XV):

InstrumentSpecification psh = new InstrumentSpecification(
    "PSH",              // ISA-5.1 symbol
    "High Pressure Switch",  // service description
    "DI",               // I/O type
    2                   // SIL rating (IEC 61508)
);

Safety instruments with a SIL rating > 0 are automatically marked as safetyRelated = true and their output signal defaults to "Discrete 24VDC".

ISA-5.1 Symbol Mapping

The constructor auto-detects the instrument type from the ISA symbol:

ISA Symbol Prefix Instrument Type Default Cost (USD)
PT, PI PressureTransmitter 3,500
PS PressureSwitch 3,500
TT, TI, TE TemperatureTransmitter 2,500
TS TemperatureSwitch 2,500
LT, LI LevelTransmitter 5,000
LS LevelSwitch 5,000
FT, FI, FE FlowTransmitter 8,000
AT, AE Analyser 15,000
VT VibrationTransmitter 4,000
ST SpeedTransmitter 2,000
ZT, ZS PositionTransmitter 3,000
XV SolenoidValve 6,000

I/O Types

Code Description Direction
AI Analog Input (4–20 mA from field to DCS) Field → DCS
AO Analog Output (4–20 mA from DCS to field) DCS → Field
DI Digital Input (discrete status from field) Field → DCS/SIS
DO Digital Output (discrete command to field) DCS/SIS → Field

Specification Attributes

Every InstrumentSpecification carries a complete data sheet:

Attribute Default Description
outputSignal "4-20mA HART" Output protocol
connectionSize "1/2 NPT" Process connection
material "316SS" Wetted parts material
hazardousAreaZone "Zone 1" Area classification
exProtection "Ex ia IIC T4 Ga" Explosion protection marking

2. InstrumentList

The InstrumentList collects all instruments for one equipment item and provides I/O counting, safety instrument counting, cost aggregation, and automatic tag number generation.

InstrumentList list = new InstrumentList("V-101");
list.add(new InstrumentSpecification("PT", "Pressure", 0.0, 100.0, "bara", "AI"));
list.add(new InstrumentSpecification("TT", "Temperature", 0.0, 200.0, "degC", "AI"));
list.add(new InstrumentSpecification("PSH", "High Pressure", "DI", 2));

System.out.println("AI count: " + list.getAnalogInputCount());   // 2
System.out.println("DI count: " + list.getDigitalInputCount());  // 1
System.out.println("Total I/O: " + list.getTotalIOCount());      // 3
System.out.println("Safety: " + list.getSafetyInstrumentCount()); // 1
System.out.println("Cost: " + list.getTotalCostUSD() + " USD");

Tag numbers are auto-generated in the format <ISA Symbol>-<counter> (e.g. PT-1, PT-2, TT-3) unless manually assigned before adding to the list.

3. InstrumentDesign (Base Class)

The base InstrumentDesign class mirrors ElectricalDesign:

Property Default Description
hazardousAreaZone "Zone 1" IEC 60079-10 zone classification
protectionConcept "Ex ia" Explosion protection (intrinsic safety)
instrumentStandard "IEC" "IEC" or "ISA"
includeSafetyInstruments true Whether to add SIS instruments
defaultSilLevel 2 Default SIL for safety instruments

API

InstrumentDesign design = new InstrumentDesign(equipment);
design.setHazardousAreaZone("Zone 2");
design.setDefaultSilLevel(3);
design.calcDesign();

int ioCount = design.getTotalIOCount();
double cost = design.getEstimatedCostUSD();
String json = design.toJson();

4. Equipment-Specific Instrument Designs

4.1 Separator

A separator vessel requires pressure, temperature, and level control plus safety trips:

Instrument ISA Symbol I/O SIL Notes
Process Pressure PT AI — Voted pair (2 transmitters)
Process Pressure (Redundant) PT AI —  
High Pressure Switch PSH DI 2 Overpressure trip
Process Temperature TT AI —  
Liquid Level LT AI — Voted pair (2 transmitters)
Liquid Level (Redundant) LT AI —  
High Level Switch LSH DI 2 Overflow protection
Low-Low Level Switch LSLL DI 2 Pump protection
Level Control Valve Position ZT AI —  
Pressure Control Valve Position ZT AI —  

Three-phase separators add:

Instrument ISA Symbol I/O Notes
Water/Oil Interface Level LT AI Interface level transmitter
Water Dump Valve Position ZT AI   
Separator sep = new Separator("HP Sep", feed);
sep.run();

SeparatorInstrumentDesign instrDesign =
    (SeparatorInstrumentDesign) sep.getInstrumentDesign();
instrDesign.calcDesign();

InstrumentList list = instrDesign.getInstrumentList();
System.out.println("Instruments: " + list.size());  // ~10
System.out.println("Safety: " + list.getSafetyInstrumentCount());  // 3
System.out.println(instrDesign.toJson());

4.2 Compressor

Compressor instrumentation follows API 617 (centrifugal compressors) and API 670 (machinery protection):

Instrument ISA Symbol I/O SIL Notes
Suction Pressure PT AI —  
Discharge Pressure PT AI —  
Differential Pressure (Surge) PDT AI — Anti-surge detection
Discharge Overpressure Trip PSHH DI 2  
Suction Temperature TT AI —  
Discharge Temperature TT AI —  
Bearing n Temperature TT AI — Per bearing (default 2)
Discharge Overtemperature Trip TSHH DI 2  
Suction Flow (Anti-Surge) FT AI —  
Anti-Surge Valve Output FCV AO —  
Bearing n Vibration X VT AI — API 670 X-Y probes
Bearing n Vibration Y VT AI — Per bearing (default 2)
High Vibration Trip VSHH DI 2  
Shaft Speed ST AI —  
Lube Oil Pressure PT AI —  
Low Lube Oil Pressure Trip PSLL DI 2  

With 2 bearings, a compressor has ~18 instruments including 5 safety trips.

Compressor comp = new Compressor("1st Stage", feed);
comp.setOutletPressure(50.0);
comp.run();

CompressorInstrumentDesign instrDesign =
    (CompressorInstrumentDesign) comp.getInstrumentDesign();
instrDesign.setNumberOfBearings(3);  // Override default of 2
instrDesign.setIncludeAntiSurge(true);
instrDesign.calcDesign();

System.out.println("Total I/O: " + instrDesign.getTotalIOCount());
System.out.println(instrDesign.toJson());

4.3 Heat Exchanger

The design auto-detects the heat exchanger type from the equipment class:

Equipment Class Detected Type Additional Instruments
HeatExchanger SHELL_AND_TUBE Utility side TT×2, PT
Cooler AIR_COOLER Ambient TT, fan ST, fan VT
Heater ELECTRIC_HEATER Element TT, element TSHH

All types share a common instrument set:

Instrument ISA Symbol I/O Notes
Process Inlet Temperature TT AI  
Process Outlet Temperature TT AI  
Process Inlet Pressure PT AI  
Process Outlet Pressure PT AI  
Process Side dP PDT AI Fouling/blockage detection
Overtemperature Trip TSHH DI SIL-rated 
Heater heater = new Heater("Electric Heater", feed);
heater.setOutTemperature(273.15 + 80.0);
heater.run();

HeatExchangerInstrumentDesign instrDesign =
    (HeatExchangerInstrumentDesign) heater.getInstrumentDesign();
instrDesign.calcDesign();

System.out.println("Type: " + instrDesign.getHeatExchangerType());
System.out.println("Instruments: " + instrDesign.getInstrumentList().size());

4.4 Pipeline

Pipeline instrumentation includes pressure/temperature monitoring, flow metering, pig detection, and leak detection:

Instrument ISA Symbol I/O SIL Notes
Inlet Pressure PT AI —  
Outlet Pressure PT AI —  
Overpressure Trip PSHH DI 2  
Inlet Temperature TT AI —  
Outlet Temperature TT AI —  
Pipeline Flow FT AI — Custody/operational metering
Low Pressure (Leak Detection) PSLL DI 2  
Pig Signaller Inlet ZS DI —  
Pig Signaller Outlet ZS DI —   
AdiabaticPipe pipe = new AdiabaticPipe("Export Line", feed);
pipe.setLength(50000.0);
pipe.setDiameter(0.508);
pipe.run();

PipelineInstrumentDesign instrDesign =
    (PipelineInstrumentDesign) pipe.getInstrumentDesign();
instrDesign.setIncludePigDetection(true);
instrDesign.setIncludeLeakDetection(true);
instrDesign.calcDesign();

System.out.println("Total I/O: " + instrDesign.getTotalIOCount());

4.5 Valve

All valves get basic position feedback. Safety/ESD valves (auto-detected from class name) add a trip solenoid and limit switches:

Control valve:

Instrument ISA Symbol I/O Notes
Valve Position ZT AI Position transmitter
Valve Positioner Output ZC AO I/P converter or digital positioner

Safety / ESD valve (adds):

Instrument ISA Symbol I/O SIL Notes
Trip Solenoid XV DO 2 De-energise to trip
Open Limit Switch ZSO DI —  
Closed Limit Switch ZSC DI —  

Auto-detection recognises ESDValve, HIPPSValve, and BlowdownValve as safety valves.

ThrottlingValve valve = new ThrottlingValve("PCV-101", feed);
valve.setOutletPressure(30.0);
valve.run();

ValveInstrumentDesign instrDesign =
    (ValveInstrumentDesign) valve.getInstrumentDesign();
instrDesign.calcDesign();  // gets ZT + ZC (2 instruments)

// Force safety valve mode
instrDesign.setSafetyValve(true);
instrDesign.calcDesign();  // now gets ZT + ZC + XV + ZSO + ZSC (5 instruments)

5. System-Level Instrument Design

SystemInstrumentDesign aggregates all equipment instrument designs across a ProcessSystem and sizes the DCS/SIS control system infrastructure.

DCS and SIS Cabinet Sizing

System Channels/Card Cards/Cabinet Notes
DCS 16 16 Process (non-safety) I/O
SIS 8 8 Safety-related I/O (redundant)
Marshalling — — 1 cabinet per ~200 I/O channels

Cost Estimation Defaults

Item Unit Cost
DCS I/O channel 500 USD
SIS I/O channel 1,500 USD
DCS cabinet 50,000 USD
SIS cabinet 80,000 USD
Marshalling cabinet 15,000 USD

Usage

ProcessSystem process = new ProcessSystem();
// ... add equipment ...
process.run();

SystemInstrumentDesign sysInstr = process.getSystemInstrumentDesign();
sysInstr.calcDesign();

// Access results
System.out.println("Total instruments: " + sysInstr.getTotalInstruments());
System.out.println("Total I/O: " + sysInstr.getTotalIO());
System.out.println("  AI: " + sysInstr.getTotalAI());
System.out.println("  AO: " + sysInstr.getTotalAO());
System.out.println("  DI: " + sysInstr.getTotalDI());
System.out.println("  DO: " + sysInstr.getTotalDO());
System.out.println("Safety I/O: " + sysInstr.getTotalSafetyIO());
System.out.println("DCS cabinets: " + sysInstr.getDcsCabinets());
System.out.println("SIS cabinets: " + sysInstr.getSisCabinets());
System.out.println("Marshalling cabinets: " + sysInstr.getMarshallingCabinets());
System.out.println("Total cost: " + sysInstr.getTotalInstrumentCostUSD() + " USD");

// Full JSON report
System.out.println(sysInstr.toJson());

The JSON output includes:

6. ProcessSystem Integration

The instrument design integrates with ProcessSystem via two hooks on ProcessEquipmentInterface:

Method Description
getInstrumentDesign() Returns the equipment’s instrument design (creates on first call for lazy-init equipment)
initInstrumentDesign() Explicitly initialises the instrument design

Equipment Initialisation

Equipment Init Mode Notes
Separator Eager Created in constructor
Compressor Eager Created in constructor
Heater / Cooler Lazy Created on first getInstrumentDesign() call
AdiabaticPipe Lazy Created on first getInstrumentDesign() call

Complete Workflow Example

// Build process
SystemInterface gas = new SystemSrkEos(273.15 + 25.0, 60.0);
gas.addComponent("methane", 0.85);
gas.addComponent("ethane", 0.10);
gas.addComponent("propane", 0.05);
gas.setMixingRule("classic");

ProcessSystem process = new ProcessSystem();

Stream feed = new Stream("Feed", gas);
feed.setFlowRate(50000.0, "kg/hr");
process.add(feed);

Separator hpSep = new Separator("HP Separator", feed);
process.add(hpSep);

Compressor comp = new Compressor("Export Compressor",
    hpSep.getGasOutStream());
comp.setOutletPressure(120.0);
process.add(comp);

Cooler afterCooler = new Cooler("Aftercooler",
    comp.getOutletStream());
afterCooler.setOutTemperature(273.15 + 40.0);
process.add(afterCooler);

// Run process
process.run();

// Get plant-wide instrument summary
SystemInstrumentDesign sysInstr = process.getSystemInstrumentDesign();
sysInstr.calcDesign();

System.out.println("=== Plant Instrument Summary ===");
System.out.println("Total instruments: " + sysInstr.getTotalInstruments());
System.out.println("Total I/O: " + sysInstr.getTotalIO());
System.out.println("DCS cabinets: " + sysInstr.getDcsCabinets());
System.out.println("SIS cabinets: " + sysInstr.getSisCabinets());
System.out.println("Total CAPEX: $" + sysInstr.getTotalInstrumentCostUSD());
System.out.println(sysInstr.toJson());

7. Applicable Standards

Standard Scope Used By
ISA-5.1 Instrument identification and symbols InstrumentSpecification
ISA-18.2 Alarm management InstrumentDesign
ISA-20 Instrument specification forms InstrumentSpecification
IEC 61508 Functional safety — SIL levels InstrumentSpecification (SIL rating)
IEC 61511 Safety instrumented systems (SIS) for process industry SystemInstrumentDesign (SIS sizing)
IEC 60079 / ATEX Hazardous area classification InstrumentDesign (Ex protection)
API 670 Machinery protection systems (vibration) CompressorInstrumentDesign (VT probes)
API 617 Centrifugal compressor instrumentation CompressorInstrumentDesign

8. Class Reference

Class Package Description
InstrumentDesign process.instrumentdesign Base class — hazardous area, SIL, instrument list
InstrumentSpecification process.instrumentdesign Single instrument data sheet entry (ISA-5.1)
InstrumentList process.instrumentdesign Instrument collection with I/O counting and cost
InstrumentDesignResponse process.instrumentdesign JSON serialisation helper
SeparatorInstrumentDesign process.instrumentdesign.separator Separator-specific (PT, LT, PSH, LSH, LSLL)
CompressorInstrumentDesign process.instrumentdesign.compressor Compressor-specific (API 670/617 suite)
HeatExchangerInstrumentDesign process.instrumentdesign.heatexchanger Heat exchanger — auto-detects S&T / air cooler / electric
PipelineInstrumentDesign process.instrumentdesign.pipeline Pipeline (pig detection, leak detection, metering)
ValveInstrumentDesign process.instrumentdesign.valve Valve (position, positioner, solenoid, limit switches)
SystemInstrumentDesign process.instrumentdesign.system Plant-wide aggregation, DCS/SIS cabinet sizing