Views: 135 Author: Site Editor Publish Time: 2026-10-21 Origin: Site
1. The Industry Challenge: Signal Safety in Hazardous Atmospheres
In chemical processing, refining, and oil & gas operations, process control environments present extreme electrical and safety risks. Measuring critical variables—such as reaction kettle temperatures, vessel pressures, and flow rates—requires field instruments installed directly inside hazardous classified locations (Zone 0, Zone 1, or Zone 2 / Division 1 and 2).
In a specialty chemical manufacturing plant in Western Europe, maintenance teams faced recurring operational challenges with their batch reaction kettle temperature monitoring loops:
Hazardous Environment: Reaction vessels operating in Zone 1 (Gas Group IIC, T6) with flammable solvent vapors.
Legacy Equipment: Aging Zener diode barriers used to connect field thermocouples (TC) and RTD (Pt100) sensors to the control room DCS.
Site Pain Points: Intermittent temperature signal drift, high ground loop susceptibility, and the mandatory requirement for a dedicated, low-impedance intrinsic safety (IS) ground bed—which was increasingly difficult to maintain at required ohmic values during seasonal soil moisture shifts.
A single false temperature spike could trip high-level emergency interlocks, causing costly batch dumps. The plant required a modern, certified explosion-proof signal conditioning architecture that eliminated dedicated IS grounding requirements while ensuring full compliance with European safety directives.
2. Galvanic Isolation Barrier vs. Zener Barrier: Why Facilities Are Upgrading
When designing intrinsically safe (IS) loops under IEC/EN 60079-11, engineers must choose between passive Zener barriers and active Galvanic isolation barriers.
ZENER BARRIER vs GALVANIC ISOLATION BARRIER |
ZENER BARRIER: [ Field Sensor ] <=== Direct Wire Connection ===> [ Safety Ground ] ===> [ DCS ] * REQUIRES dedicated high-integrity IS earth ground (<1 Ω). * Vulnerable to ground loops & common-mode voltage spikes.
GALVANIC ISOLATOR (Qidian GLK Series): [ Field Sensor ] <--- Ex ia Isolation Transformer ---> [ Control Room DCS ] * NO dedicated IS ground bed required. Ground loop paths physically broken. |
Key Differences Comparison
Feature / Criterion | Legacy Zener Barrier | GLK Galvanic Isolator | Operational Advantage |
Dedicated IS Grounding | Mandatory (< 1Ωground bed) | Not Required | Saves thousands in grounding grid maintenance |
Ground Loop Immunity | Poor (direct electrical path) | Total Immunity 2500V AC isolation) | Eliminates signal noise & zero-point drift |
Signal Calibration | Sensitive to loop impedance | High Precision ( ±0.1%F.S.) | Maintains accurate Pt100/ TC scaling |
Cabinet Density | Requires ground busbars | Compact DIN-rail mounting | Reduces panel space by over 30% |
By upgrading to Qidian QD-Ex Series Galvanic Isolators, the chemical plant completely decoupled the field instrument ground from the control room DCS ground, eliminating stray ground currents without building a costly new IS earth grid.
3. Deployment Architecture: Zone 1 Boundary Setup
The project architecture separated field devices in the explosion-hazardous zone from receiving automation hardware in the safe control room:
Selected Equipment Specifications (Qidian GLK Series)
Explosion Protection Marking: Ex II (1) G [Ex ia Ga] IIC
Certifications: ATEX Directive 2014/34/EU, IECEx, CE, and SIL2 functional safety ratings.
Field Sensor Support: Universal input configurable for $\text{Pt100}$, $\text{Cu50}$ RTDs, and Type K, J, T, E thermocouples.
Dielectric Breakdown Withstand: 2500V ACbetween Input, Output, and Auxiliary 24V DC Power terminals.
4. Operational Results: Measured Impact in Process Control
Following retrofitting across 48 reaction kettle temperature loops, the plant achieved immediate operational stability:
Zero Ground Fault Alarms: Eliminating Zener barriers completely cleared ground fault alarms on the DCS diagnostic bus.
Extended Calibration Intervals: Temperature measurement drift was reduced from ±2.5℃ per quarter to within 0.2℃ over a 12-month period.Simplified Maintenance:
Calibration can be performed safely from the control room panel without entering the classified explosive atmosphere.
5. Application Matrix Across Upstream, Midstream & Downstream Oil & Gas
Intrinsically safe isolation is equally vital across the oil and gas value chain:
Qidian Signal Isolators in Oil & Gas Applications:
Industry Sector | Typical Application Loop | Hazardous Area Rating | Recommended Qidian Series | Key Requirement |
Upstream (Exploration) | Wellhead RTU & SCADA telemetry | Zone 1 / Div 1 (Ex ia) | QD-6/8 Series | Wide temperature range (-40℃ to +85℃) |
Midstream (Transport) | Long-distance pipeline flowmeters | Zone 2 / Non-Hazardous | GLG / GLK Series | Long-distance 4–20mA HART pass-through |
Downstream (Refining) | Tank farm level & temperature | Zone 0 / Zone 1 | QD-6/8 Series | SIL2 functional safety & ATEX/IECEx |
6. Frequently Asked Questions
Q1: Do Qidian QD-Ex series isolators require an isolated intrinsically safe ground bus in the cabinet?
No. Unlike Zener barriers, galvanic isolators use internal high-frequency transformers and optocouplers to provide complete galvanic separation, meaning no dedicated IS ground connection is necessary.
Q2: What is the difference between Ex ia and Ex ib protection levels?
Ex ia offers the highest protection level, ensuring safety even with two independent simultaneous component faults (suitable for Zone 0 and Zone 1). Ex ib remains safe with a single fault (suitable for Zone 1 and Zone 2). Qidian QD-Ex barriers carry Ex ia ratings for maximum safety coverage.
