Detcon FP-100 Manuel d'utilisateur télécharger pdf (Page 6)

Model FP-100

FP-100 Instruction Manual Rev. 0.0 Page 2 of 30

Principle of Operation

Method of detection is by diffusion/adsorption. Air and combustible gases pass through a sintered stainless

steel filter and contact the heated surface of both the active and reference detectors. The surface of the active

detector promotes oxidation of the combustible gas molecules while the reference detector has been treated not

to support this oxidation. The reference detector serves as a means to maintain zero stability over a wide range

of temperature and humidity.

When combustible gas molecules oxidize on the surface of the active detector, heat is generated, and the

resistance of the detector changes. Electronically, the detectors form part of a balanced bridge circuit. As the

active detector changes in resistance, the bridge circuit unbalances. This change in output is conditioned by

the amplifier circuitry, which is an integral part of the sensor design. The response and clearing characteristics

of the sensor are rapid and provide for the continuous and accurate monitoring of ambient air conditions.

Sensor

Cell

Zero

Adjust

Output

Input

Voltage

Compensator /

Reference Bead

Detector /

Active Bead

Figure 3 Wheatstone Bridge

Performance Characteristics

The detector elements maintain good sensitivity to combustible gas concentrations in the Lower Explosive

Limit (LEL) range, as shown in the response curves in Figure 4. However, for gas concentrations significantly

above the LEL range (100% LEL = 5% by volume Methane), the bridge output begins to decrease.

Ambiguous readings above the LEL range dictate that alarm control logic be of the latching type, wherein

alarms are held in the “ON” position until reset by operations personnel.

Figure 4 Response Curves

1.2 Modular Mechanical Design

The Model FP-100 Sensor Assembly is completely modular and is made up of four parts (See Figure 5 for

Assembly Breakaway):

1) FP-100 Intelligent Transmitter Module (ITM)

2) Intelligent Plug-in Sensor (varies by detector type)

3) 100 Series Bottom Housing Assembly

4) Splash Guard.

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Detcon FP-100 Manuel d'utilisateur Page 6