Detcon FP-624C Manuel d'utilisateur télécharger pdf (Page 5)

3.1.2 Characteristics

The detector elements maintain good sensitivity to combustible gases in air in the lower explosive limit range, as shown in

the response curve illustration below. However, for gas concentrations above the LEL range, the bridge output decreases.

Ambiguous readings above LEL range conditions dictate that alarm circuitry be of the latching type wherein alarms are

held in the “on” position until reset by operations personnel.

The performance of the detector elements may be temporarily impaired by operation in the presence of sub-

stances described as inhibitors. These are usually volatile substances containing halogens and the detectors may

recover after short periods of operation in clean air. When the inhibiting substance produces a permanent effect on

the catalyst with a catastrophic reduction in sensitivity, the detector is said to be poisoned. Examples of poisons

are; silicone oils and greases, anti-knock petrol additives and phosphate esters. Activated carbon filters will provide

adequate protection from poisoning in the majority of cases.

3.2 APPLICATION

Model FP-624C MicroSafe™ sensors are designed to detect and monitor combustible gas in ambient air in the range of

0-100% LEL. Minimum sensitivity and scale resolution is 1%. Operating temperature range is -40° F. to +175° F. While

the sensor is capable of operating outside these temperatures, performance specifications are verified within the limit.

3.2.1 Sensor Placement/Mounting

Sensor location should be reviewed by facility engineering and safety personnel. Area leak sources and perimeter mounting

are typically used to determine number and location of sensors. The sensors are generally located 2 - 4 feet above grade.

Model FP-624C Combustible Gas Sensor PG.5

% Methane in Air Concentration

100

020406080

Bridge Output %

20 40 60 80 100

% LEL (lower explosive limit)

mA DC Signal Output

Response Curve

Functional

Block

Diagram

Functional

Block

Diagram

Analog 4-20 mA Out

Power In

Relays Out

Pre-Amp Display

Temperature

Compensation

Alarm & Fault

Relays

RS-485 & 4-20mA

Micro-

processor

Transmitter

Power Supply

Sensor

Element

I/O Circuit

Protection

Serial RS-485 Out

2.2V

Zero

utput

Detector/Active

Compensator/Reference

1 2 3 4 5 6 7 8 9 10 ... 25 26

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Detcon FP-624C Manuel d'utilisateur Page 5

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