Bacharach 2772-0803 manual System Description, Basic Principles

REMOTE INTELLIGENT SENSOR - AREA MONITOR

1 INTRODUCTION

1.1SYSTEM DESCRIPTION

A range of Remote Intelligent Sensors (RIS) are available. Each is designed to measure low concen- trations of a specific gas. Multiple RIS systems can be connected into a control network to provide an area monitoring capability with central supervision.

The RIS is a single point, microprocessor

controlled, instrument for use in a fixed location. Two RIS versions were produced (see Supplement A for units built before April '92).

The RIS is housed in an environmentally sealed enclosure and is line-powered, via a DC power supply, for continuous monitoring. An internal backup battery is provided as protection against power interruptions.

The standard system provides clear visual indication of status, concentration level, 4-20 ma analog output, gas, and fault alarm conditions. TWA’s, 15 minute and 8 hour, are displayed at the touch of a keyboard button.

Reliable and effective operation is assured by on-line self-diagnostic routines. An easy-to-use TEST Mode allows key parameters to be checked and adjusted.

Optional features provide storage, and printout, of up to one week’s data points, two independently selectable (via keypad) alarm relays with a separate fault indication relay and a hardware selectable 0-1 VDC analog output (Sections 2.4.5 & 2.7).

1.2BASIC PRINCIPLES

A measured sample volume is drawn into the RIS and passed through a chemically impregnated paper tape. The tape reacts to the presence of a specific gas by developing a stain whose intensity is proportional to the sample concentration.

A beam of light is bounced off the tape and the reflected light is measured. The difference in reflected light values, developed before and after the stain, is used to calculate stain intensity, enabling the sampled gas concentration to be determined.

The measurement of low gas concentration levels takes place during a fixed four minute sample period. If the sample concentration rises above a predetermined value, the operating mode changes and the system measures the time taken for a given stain value to develope.

This technique provides a wide dynamic range, good resolution and a rapid response to rising gas levels. In addition, the tape never becomes saturated which ensures accurate measurement, and toxic gases are prevented from breaking through the tape into the system. A double track, tape management system gives maximum tape economy.

This combination of operating features gives long tape cassette life at low sampling levels, and a rapid response with excellent tracking of short term peaks as levels rise.

The detection of a gas concentration that is higher than the user-adjustable alarm set point, results in a highly visible warning on the RIS's large custom display. In addition, local and remote external warning devices or systems can be activated via interface signals.

1.3GENERAL DESCRIPTION

1.3.1ENCLOSURE. The instrument is contained within a tough, IP-55 rated, enclosure that is suitable for installation inside and out. A large liquid crystal display (LCD) is mounted in the front face of the door next to a membrane keyboard that is used for programming certain functions.

Figure 1-1. Enclosure

The door is hinged on one side and secured shut by two screw fasteners, which are opened with a special key to discourage unauthorized tampering. The door hinges are easily disengaged and removal of the door from the base is quick and simple, should this ever be required.

Adoor-open fault display icon, and relay output provide warnings and help ensure that RIS is only operated when the enclosure is secured shut.

There are threaded mounting holes in the base of the enclosure. The mounting brackets are sup- plied with the system.

1.3.2CABLE GLANDS. Three sealed glands are provided for cable entry and exit. A socket is provided at one end to allow the connection of an optional printer.

1.3.3MAIN SYSTEM BOARD. The board is mounted on the rear face of the door and is acces- sible when the door is open. The red push-button TEST Mode switch is in the bottom left-hand corner, as viewed with the door open.

Instruction 2772-0803 Page 1-1