™
detcon inc.
Detcon MicroSafe
FP-624C Combustible Gas Sensor (0-100% LEL)
Operator’s Installation & Instruction Manual
May 18, 2010 • Document #2246 • Revision 7.1
CAUTION:
Before operating the Model FP-624C sensor, read this manual thoroughly and verify that the
configuration of default factory settings are appropriate and correct for your application. The
settings include: Target gas and calibration gas (section 3.7), relay contact outputs (section
3.5.5d), alarm settings (section 3.5.5e and 3.10), and RS-485 ID (section 3.5.5f and 3.12).
Table of Contents
3.0 Description
3.1 Principle of Operation
3.2 Application
3.3 Specifications
3.4 Operating Software
3.5 Installation
3.6 Start-up
3.7 Target Gas and Calibration Gas Selection
3.8 Calibration
3.9 Status of Programming, Alarms, Calibration Level, RS-485 ID, and Sensor Life
3.10 Programming Alarms
3.11 Program Features
3.12 RS-485 Protocol
3.13 Display Contrast Adjust
3.14 Trouble Shooting Guide
3.15 Spare Parts List
3.16 Warranty
3.17 Service Policy
3.18 Software Flow Chart
Model FP-624C Combustible Gas Sensor PG.2
3.0 DESCRIPTION
Alumina Bead
Platinum Wire
Catalyst
Construction of
Detector Bead
Sintered Stainless Steel Can
Header
Gold Plated Pins
Beads
Detcon MicroSafe™ Model FP-624C, combustible gas sensors are non-intrusive
“Smart” sensors designed to detect and monitor combustible gas in air over the
range of 0-100% lower explosive limit (LEL). One of the primary features of the sensor is its method of automatic calibration which guides the user through each step
via instructions displayed on the backlit LCD. The sensor features f ield adjustable,
fully programmable alarms and provides relays for two alarms plus fault as standard.
The sensor comes with two different outputs: analog 4-20 mA, and serial RS-485.
These outputs allow for greater flexibility in system integration and installation. The
microprocessor supervised electronics are packaged as a plug-in module that mates
to a standard connector board. Both are housed in an explosion proof condulet that
includes a glass lens window which allows for the display of sensor readings as well
as access to the sensor’s menu driven features via a hand-held programming magnet.
The sensor technology is of the catalytic pellistor type. Catalytic pellistors show
a good response to a long list of combustible gases. The technique is referred to as
non-selective and may be used for the detection and monitoring of target combustible gases. Model FP-624C sensors are specifically designed to be resistive to poisons such as sulfides, chlorides and silicone. The sensors are characteristically stable
and capable of providing reliable performance for periods exceeding 5 years in most
industrial environments.
3.0.1 Catalytic Detector
The catalytic detector is supplied as a matched pair of elements mounted in a plug-in replaceable housing. One element is an active catalytic detector and the other is a non-active compensating element. Each element consists of a
fine platinum wire embedded in a bead of alumina. A catalytic mixture is applied to the detecting element while the
compensating element is treated so that catalytic oxidation of gas does not occur. The beads are mounted in a plug-in
module that is enclosed by a sintered porous stainless steel flame arrestor. The plug-in sensor module uses gold plated pins and mounts inside the stainless steel sensor head via mating gold plated sockets.
3.0.2 Microprocessor Control Circuit
The control circuit is microprocessor based and is packaged as a plug-in field replaceable module, facilitating easy
replacement and minimum down time. Circuit functions include a basic sensor pre-amplifier, sensor temperature
control, on-board power supplies, microprocessor, back lit alpha numeric display, alarm status LED indicators, magnetic programming switches, an RS-485 communication port, and a linear 4-20 mA DC output.
Model FP-624C Combustible Gas Sensor PG.3
3.0.3 Base Connector Board
NC
ALARM 1
WHT
BLK
YEL
BLU
MA
V
DC Power In
N
O
NC
N
O
NC
N
O
NO/NC
COM
NO/NC
COM
NO/NC
COM
FAULT ALM -2 ALM -1
Alarm Dry Contacts
ALARM 2
FAULT
R1
A
B
A
B
4
-20 mA Output
R
S-485 In
RS-485 Out
Optional Voltage
Developing Resistor
Use 250 ohm 1/4w
JUMPERS
UN-USED
J
umper Programmable Alarm Outputs
Normally Open or Normally Closed
Sensor
Place un-used alarm programming
jumper tabs here
d
etcon inc.
Program Switch #2
FLT
A
LM
1CAL
M
icroSafe™ LEL Gas Sensor
HOUS TON, TEX AS
P
GM 2
PGM 1
A
LM
2
MODEL FP-624C
C
ONTRAST
A
larm & Cal LEDs
P
rogram Switch #1
Menu Driven Display
Plug-in Microprocessor Control Circuit
Display Contrast Adjust
The base connector board is mounted in the
explosion proof enclosure and includes: the
mating connector for the control circuit,
reverse input and secondary transient suppression, input filter, alarm relays, lugless terminals for all field wiring, and a terminal strip
for storing unused programming jumper tabs.
The alarm relays are contact rated 5 amps @
125 VAC, 5 amps @ 30 VDC and coil rated
at 24 VDC. Gold plated program jumpers are
used to select either the normally open or
normally closed relay contacts.
3.0.4 Explosion Proof Enclosure
The sensors are packaged in a cast metal explosion proof enclosure. The enclosure is fitted with a threaded cover
that has a glass lens window. Magnetic program switches located behind the transmitter module face plate are activated through the lens window via a hand-held magnetic programming tool allowing non-intrusive operator interface with the sensor. All calibration and alarm level adjustments can be accomplished without removing the cover
or declassifying the area. Electrical classification is Class I; Groups B, C, D; Div. 1.
3.1 PRINCIPLE OF OPERATION
Method of detection is by a controlled rate of diffusion/adsorption. Air and gas diffuse through a sintered stainless
steel filter and contact both the active and reference detector beads. The surface of the active detector promotes
oxidation of the combustible gas molecule while the reference detector has been treated not to support this oxidation. The reference detectors serve as a means to maintain zero stability over a wide operating temperature range.
When combustible gas molecules oxidize on the surface of the active detector, heat is generated, effectively changing the electrical conductance of the active detector. Electronically, the detectors form part of a balanced bridge circuit. As the active detector changes in electrical conductance, the bridge circuit unbalances. This change in output is
conditioned by amplifier circuits that are an integral part of the assembly. The sensor response and clearing characteristics are quite rapid resulting in a method of continuous and accurate monitoring of ambient air conditions.
Model FP-624C Combustible Gas Sensor PG.4
3.1.2 Characteristics
% Methane in Air Concentration
0
20
40
60
80
100
020406080
Bridge Output %
0
4
8
12
16
20
20 40 60 80 100
% LEL (lower explosive limit)
mA DC Signal Output
Response Curve
Response Curve
Functional
Block
Diagram
Functional
Block
Diagram
Analog 4-20 mA Out
Power In
Relays Out
Pre-Amp Display
Tem per atu re
Compensation
Alarm & Fault
Relays
RS-485 & 4-20mA
Micro-
processor
Tran smit ter
Power Supply
Sensor
Element
I/O Circuit
Protection
Serial RS-485 Out
2.2V
Zero
S
et
O
utput
Detector/Active
Compensator/Reference
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 substances 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
3.2.2 Response to Different Gases
An attractive feature of the catalytic detector elements is their almost universal response to lower explosive limits of
hydrocarbons. Most detectable gases produce a similar output, however the signal amplitudes differ. The table in
section 3.7 lists theoretical factors (K factors) for different gases which are a measure of their signal amplitude as
compared to methane which has a K factor of 1.00. Since these factors are theoretical, they will only give a guide to
the response expected in other gases. The Model FP-624C sensor can be configured to detect any of the listed gases.
The gas selected for detection is referred to as the target gas. The sensor can also be configured to allow the user to
calibrate with a listed gas other than the target gas. This selection is referred to as the calibration gas. Unless otherwise specified, Model FP-624C sensors are configured to detect methane and are calibrated with methane to a scale
of 0-100% LEL. Refer to section 3.7 for details.
3.3 SPECIFICATIONS
Method of Detection
Catalytic detector diffusion/adsorption
Measurment Range
0-100% (lower explosive limit) LEL
Accuracy/Repeatability
± 3% LEL in 0-50% LEL Range; ± 5% LEL in 51-100% LEL Range
Response/Clearing Time
T50 <10 seconds; T90 <30 seconds
Zero Drift
< 5% per year
Operating Temperature Range
-40° to +175° F; -40° to +75°C
Operating Humidity Range
0-99% non-condensing
Output
3 relays (alarm 1, alarm 2, and fault) contact rated 5 amps @ 125 VAC, 5 amps @ 30 VDC;
Linear 4-20 mA DC; RS-485 Modbus™
Input Voltage
22-28 VDC
Power Consumption
Normal operation = 84 mA (2 watts); Full alarm = 128 mA (3.1 watts)
Electrical Classification
Explosion Proof; Class I; Div. 1; Groups B, C, D
Safety Approvals
CSA/NRTL (US OSHA Certified)
Sensor Warranty
2 year conditional
3.4 OPERATING SOFTWARE
Operating software is menu listed with operator interface via the two magnetic program switches located under the
face plate. The two switches are referred to as “PGM 1” and “PGM 2”. The menu list consists of 3 items which
include sub-menus as indicated below. (Note: see the last page of this manual for a complete software f low chart.)
01. Normal Operation
a) Current Status
02. Calibration Mode
a) Zero
b) Span
03. Program Menu
a) Program Status
b) Alarm 1 Level
Model FP-624C Combustible Gas Sensor PG.6
c) Alarm 2 Level
d) Target gas selection (gas K factor)
e) Calibration gas selection (cal K factor)
f) Calibration Level
g) Set Bridge Volts
3.4.1 Normal Operation
In normal operation, the display tracks the current status of the sensor and gas concentration and appears as:
“0 % LEL”. The mA current output corresponds to the monitoring level and range of 0-100% = 4-20 mA.
3.4.2 Calibration Mode
Calibration mode allows for sensor zero and span adjustments. “1-ZERO 2-SPAN”
3.4.2.1 Zero Adjustment
Zero is set in ambient air with no combustible gas present or with zero gas applied to the sensor. “AUTO ZERO”
3.4.2.2 Span Adjustment
Unless otherwise specified, span adjustment is performed at 50% LEL methane in air. “AUTO SPAN”
3.4.3 Program Mode
The program mode provides a program status menu, allows for the adjustment of alarm set point levels, the selection of the target gas K factor, the selection of the calibration gas K factor and the selection of the calibration gas
level setting.
3.4.3.1 Program Status
The program status scrolls through a menu that displays:
* The gas type, range of detection and software version number. The menu item appears as: “LEL 0-100 V6.4”
* The alarm set point level of alarm 1. The menu item appears as: “ALM1 SET @ ##%”
* The alarm firing direction of alarm 1. The menu item appears as: “ALM1 ASCENDING” or descending.
* The alarm relay latch mode of alarm 1. The menu item appears as: “ALM1 NONLATCHING” or latching.
* The alarm relay energize state of alarm 1. The menu item appears as: “ALM1 DE-ENERGIZED” or energized.
* The alarm set point level of alarm 2. The menu item appears as: “ALM2 SET @ ##%”
* The alarm firing direction of alarm 2. The menu item appears as: “ALM2 ASCENDING” or descending.
* The alarm relay latch mode of alarm 2. The menu item appears as: “ALM2 LATCHING” or nonlatching.
* The alarm relay energize state of alarm 2. The menu item appears as: “ALM2 DE-ENERGIZED” or energized.
* The alarm relay latch mode of the fault alarm. The menu item appears as: “FLT NONLATCHING” or latching.
* The alarm relay energize state of the fault alarm. The menu item appears as: “FLT ENERGIZED” or deenergized.
* Identification of the target gas K factor. The menu item appears as: “GAS FACTOR #.##”
* Identification of the calibration gas K factor. The menu item appears as: “CAL FACTOR #.##”
* The calibration gas level setting. The menu item appears as: “CalLevel @ xx%”
* Identification of the RS-485 ID number setting. The menu item appears as: “485 ID SET @ ##”
* The estimated remaining sensor life. The menu item appears as: “SENSOR LIFE 100%”
3.4.3.2 Alarm 1 Level Adjustment
The alarm 1 level is adjustable over the range 10 to 90%. For combustible gas sensors, the level is factory set at
20%. The menu item appears as: “SET ALM1 @ 20%”
3.4.3.3 Alarm 2 Level Adjustment
The alarm 2 level is also adjustable over the range 10 to 90%. For combustible gas sensors, the level is factory set at
40%. The menu item appears as: “SET ALM2 @ 40%”
3.4.3.4 Target Gas Selection
The target gas K factor is adjustable over the range 0.79 to 5.65. For combustible gas sensors configured for the
detection of methane, the level is factory set at 1.00. The menu item appears as: “GAS FACTOR 1.00”
3.4.3.5 Calibration Gas Selection
The calibration gas K factor is adjustable over the range 0.79 to 5.65. For combustible gas sensors that are calibrated
using methane, the level is factory set at 1.00. The menu item appears as: “CAL FACTOR 1.00”
Model FP-624C Combustible Gas Sensor PG.7
3.4.3.6 Calibration Level Adjustment
The Calibration level is adjustable from 10% to 90% LEL. The menu item appears as: “CalLevel @ ##%”
3.4.3.7 Set Bridge Volts
For applications where the sensor is remotely mounted away from the sensor transmitter, the detector bridge voltage is
adjustable to compensate for differing wire resistances. The menu item appears as: “SET BRIDGE VOLTS”
3.5 INSTALLATION
Optimum performance of ambient air/gas sensor devices is directly relative to proper location and installation practice.
3.5.1 Field Wiring Table
Detcon Model FP-624C combustible gas sensor assemblies require three conductor connection between power supplies and host electronic controllers. Wiring designators are
single conductor resistance between sensor and controller is 10 ohms. Maximum wire size for termination in the
sensor assembly terminal board is 14 gauge.
AWG Meters Feet
20 240 800
18 360 1200
16 600 2000
14 900 3000
Note 1:
Note 2: Shielded cable may be required in installations where cable trays or conduit runs include high voltage
lines or other sources of induced interference.
Note 3: The supply of power must be from an isolating source with over-current protection as follows:
AWG
22 3A 16 10A
20 5A 14 20A
18 7A 12 25A
The RS-485 (if applicable) requires 24 gauge, two conductor, shielded, twisted pair cable between sensor and host
PC. Use Belden part number 9841. Two sets of terminals are located on the connector board to facilitate serial loop
wiring from sensor to sensor. Wiring designators are
This wiring table is based on stranded tinned copper wire and is designed to serve as a reference only.
Over-current Protection AWG Over-current Protection
(4-20 mA output)
A& B
+
(DC), –(DC) , and mA(sensor signal). Maximum
(IN) and A& B(OUT).
3.5.2 Sensor Location
Selection of sensor location is critical to the overall safe performance of the product. Five factors play an important
role in selection of sensor locations:
(1) Density of the gas to be detected
(2) Most probable leak sources within the industrial process
(3) Ventilation or prevailing wind conditions
(4) Personnel exposure
(5) Accessibility for routine maintenance
Density
heavier than air gases should be located within 2-4 feet of grade as these heavy gases will tend to settle in low lying
areas. For gases lighter than air, sensor placement should be 4-8 feet above grade in open areas or in pitched areas
of enclosed spaces.
Leak Sources
tions of the sealed type where seals may either fail or wear. Other leak sources are best determined by facility engineers with experience in similar processes.
- Placement of sensors relative to the density of the target gas is such that sensors for the detection of
- Most probable leak sources within an industrial process include f langes, valves, and tubing connec-
Model FP-624C Combustible Gas Sensor PG.8
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