Hochiki I.S. Compatible Dual Zone Monitor, ESP, Isolator CHQ-DZM(SCI)-IS

Overview

Some areas carry an explosion risk from gas, vapour or dust, and only intrinsically safe (I.S.) detectors may be used there. An I.S. device is designed so that even a fault cannot release enough energy to ignite the atmosphere.

This Hochiki module lets two zones of those I.S. detectors report to an ordinary ESP addressable fire system. The module itself stays in the safe area, with a barrier between it and the hazardous zone.

How it works

• Two conventional zones: each zone is a conventional circuit of Hochiki CDX Range I.S. detectors, monitored for short and open circuit and ended with the supplied 10 kΩ resistor.
• The barrier: a galvanic isolator or zener barrier limits the energy that can pass into the hazardous area.
• One address: the module takes a single loop address, set on DIL switches, and reports each zone's state to the panel.
• Auxiliary supply: the zones are powered from an auxiliary 24 VDC supply, not from the loop.

Where to use it

Hazardous areas are found in places such as fuel stores and solvent rooms. The hazardous-area classification and the I.S. design come first, and the detectors, barrier and cable must all suit that design.

The module itself mounts in the safe area, usually in a plant room or riser close to the barrier.

What the figures mean in practice

• 20 per zone: each zone takes up to 20 SLR-E-IS or DCD-1E-IS detectors and up to 20 CCP-E-IS manual call points. Splitting a large hazardous area across both zones keeps a fault on one zone from taking out all of it.
• 50 Ω and 0.3 µF: limits for the zone wiring. Long cable runs use these up first, so work them out at the design stage rather than on site.
• 70 mA in fire: the worst-case draw on the auxiliary supply. Add it to that supply's other loads when sizing the power supply and its battery.

Installing it

• Address first: set the loop address on the DIL switches before fixing the module.
• Call points: wire any call points at the beginning of the zone, because the zones do not support line continuity options.
• Glanded cables: for glanded cables, a CHQ-BACKBOX module back box is sold separately.
• Heavy cable: for heavy-duty cable, Hochiki recommends the SMB-1 box with the SMB-ADAPTOR plate and a CHQ-ADAPTOR.

Planning your system

Besides the module, the job needs a barrier, the I.S. detectors and call points, and an auxiliary supply. A fire alarm power supply with battery standby is the usual way to provide it.

Other interfaces sit among the fire panel modules and interfaces, and the wider Hochiki fire range covers other loop devices. The commercial fire alarm guide explains why loop devices must match the panel's protocol.

Hazardous-area work needs a competent designer and installer, and the I.S. certification must be kept intact.