Field Reference Pack

// LOTO sequence · Calibration terms · SIS basics · Hazard protection

Non-Negotiable Rules — Know These Before Touching Anything

Never open explosion-proof (XP) housing while energized — isolate power first, confirm dead, then open
Verify zero energy at the work point — not at the panel, AT the device. Power, pressure, mechanical, thermal — all four
Blind/spectacle plate = positive isolation — a closed valve is NOT positive isolation for hazardous process
Hot work permit required for any sparks or heat sources in classified hazardous areas
Write protect the transmitter configuration to prevent accidental changes during work

// LOTO SEQUENCE — CLICK EACH STEP TO MARK COMPLETE

// ENERGY TYPES — VERIFY ZERO FOR ALL THAT APPLY

ELECTRICAL

Measure VDC at device terminals. Must read 0V. Don't rely on breaker position alone.

PNEUMATIC / PROCESS PRESSURE

Vent actuator, bleed impulse lines. Confirm 0 PSI at gauge. Pressure side and reference side.

MECHANICAL

Block and brace where gravity could move equipment. Confirm valve is physically blocked open or closed as required.

THERMAL

Allow process to cool to safe temperature before contact. Hot process lines retain heat long after isolation.

// CLICK ANY TERM FOR FULL DEFINITION AND FIELD EXAMPLE

// CALIBRATION HIERARCHY

Sensor trim

→

Output trim

→

Loop calibration

Full verified chain

Loop calibration beats component calibration — it verifies the entire signal chain from sensor to DCS display, catching errors that individual component checks miss (wiring resistance, AI card offset, signal conditioning).

// SAFETY INSTRUMENTED SYSTEMS — WHAT YOU NEED TO KNOW IN THE FIELD

What SIS Does

Forces the process to a safe state when normal control fails to prevent a hazard. It is the last automated defense before something bad happens. Normal control (BPCS) = run the process
SIS = catch it when control fails
These must be INDEPENDENT — no shared sensors, logic, or valves Your job: verify the chain works — sensor sees it → logic decides → final element moves.

Key Terms

SIL — Safety Integrity Level. The required reliability. SIL 1 = 90-99% effective, SIL 2 = 99-99.9%, SIL 3 = 99.9–99.99%. SIL 1: 10–100× risk reduction
SIL 2: 100–1000× risk reduction
SIL 3: 1000–10000× risk reduction PFD — Probability of Failure on Demand. Chance the SIS fails exactly when it's needed. The number proof testing is verifying.

Proof test — Full functional test to find hidden failures. Typically 1–5 years. Must be done — don't push it.

Architecture Basics

1oo1 — One out of one. Single device trips the system. Simple but single point of failure.

1oo2 — One out of two. Either sensor trips. More sensitive, more spurious trips.

2oo3 — Two out of three. Voting system. Reduces spurious trips while maintaining safety. Most common in critical applications. Reduce common failure: use different technologies
(radar + DP for level, not two identical radars)

SIS Field Rules

Bypass = controlled risk. Document it. Get approval. Implement compensating measures. Don't leave it bypassed.

Proof test due → schedule it. Never push a proof test because it's inconvenient. That's exactly when failures are hidden.

Spurious trips → tuning problem or noise issue, not a reason to bypass. Find the cause.

Mismatched parts (wrong SIL rating sensor, wrong logic solver) = unsafe condition. Replace correctly.

// FAILURE TYPES — KNOW THESE COLD

Type	What It Means	How It's Found	Field Action
Dangerous Undetected	Hidden failure — SIS will NOT work when needed. Worst case.	Proof test only — invisible during normal operation	Prevent: regular proof testing, diagnostics coverage
Dangerous Detected	Failure caught by diagnostics — SIS trips or alarms	Automatic diagnostic alarm	Repair immediately. Treat as unsafe until fixed.
Safe Detected (Spurious)	Nuisance trip — SIS goes to safe state unnecessarily	Process upsets when no hazard existed	Find cause and fix. Don't bypass — tune or repair.
Safe Undetected	Conservative error — reading says more dangerous than reality	May go unnoticed during operation	Low risk but investigate — may mask real condition

// THE MENTAL COMPRESSION

Can it sense it → can it think → can it move → will it still work when it matters?

Your job in SIS work: verify independence (no shared failure modes), verify the final element actually strokes, and make sure proof tests are done on schedule. Everything else is detail.

// PROTECTION TYPES — WHAT EACH ONE MEANS AND THE ONE RULE THAT MATTERS

IS — INTRINSIC SAFETY

Intrinsic Safety

Concept: Limit the electrical energy to levels that cannot ignite the hazardous atmosphere — even under fault conditions. No spark can form because there isn't enough energy. Safe to work LIVE in hazardous area
Requires IS barriers to limit energy
Device AND cable must stay below barrier limits
Most 4-20mA field instruments

IS matching rule: Device + cable capacitance/inductance must stay below barrier entity parameters. Don't mix non-IS equipment in an IS loop.

XP — EXPLOSION-PROOF

Explosion-Proof

Concept: If an explosion occurs inside the housing, it is contained — the housing is strong enough to contain the blast and flame path is long enough that hot gases cool before exiting. Does NOT prevent explosion inside
Contains it so it doesn't propagate outside
Heavy, thick-walled cast enclosures
Junction boxes, conduit fittings, motors

RULE: Kill power before opening. No exceptions. An XP housing open with power = no protection at all.

Ex e — INCREASED SAFETY

Increased Safety

Concept: No sparks or excessive heat by design — enhanced construction prevents the conditions that could cause ignition from occurring in the first place. Terminal boxes, junction boxes
No intentional spark sources
Enhanced insulation and clearances
Prevent faults rather than contain them

RULE: Prevent faults. No modification. No loose connections. Enhanced construction is the protection — compromising it removes it.

NI — NON-INCENDIVE (Div 2)

Non-Incendive

Concept: Less strict than IS — safe in Division 2 areas where hazardous atmosphere is not normally present. Sparks are acceptable under normal conditions but not fault conditions. Division 2 / Zone 2 only
Normal operation: no ignition-capable sparks
Fault condition: not guaranteed
Cannot be used in Division 1 / Zone 1

RULE: Verify area classification. Non-incendive equipment is NOT safe in Division 1. Check the nameplate classification against the area classification drawing.

// T-CODES AND ENCLOSURE RATINGS — QUICK REFERENCE

T-CODES (max surface temperature)

T6	85°C max surface	Coolest running
T5	100°C max surface	Common on instruments
T4	135°C max surface	Most common rating
T3	200°C max surface	Motors, heaters
T1/T2	300–450°C max	High-temp devices

Lower T number = higher allowed surface temp. Match T-code to gas ignition temperature of the hazardous atmosphere.

ENCLOSURE RATINGS

NEMA 4X / IP66-67

Environmental protection only — not explosion protection. Waterproof and dustproof but does NOT make equipment safe in a hazardous area.

Conduit Seals

Stop flame and gas travel through conduit. Required within ~18 inches of XP enclosure entries. Must be filled with sealing compound. Never skip these.