INSTRUCTION MANUAL
DETCON, Inc.
April 23, 2012
• Document #
3598
• Revision
1.2
Detcon Model FP-624D
PGM 1
MODEL FP-624DHOUSTON,TEXAS
TM
MicroSafe LEL Gas Sensor
ALM ALM
FLT 1 2 CAL
PGM 2
FP-624D Combustible Gas Sensor
(0-100% LEL)
4055 Technology Forest Blvd, Suite 100,
The Woodlands, Texas 77381
Ph.281.367.4100 / Fax 281.298.2868
www.detcon.com
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Model FP-624D
FP-624D InstructionManual ii
Model FP-624D
Table of Contents
1. Introduction............................................................................................................................................1
1.1 Description.....................................................................................................................................1
1.2 Modular Mechanical Design...........................................................................................................3
1.3 Relay Outputs ................................................................................................................................5
2. Installation ............................................................................................................................................. 6
2.1 Operational Guidelines for Safe Use...............................................................................................6
2.2 Sensor Placement ...........................................................................................................................6
2.3 Sensor Contaminants and Interference............................................................................................7
2.4 Mounting Installation .....................................................................................................................8
2.5 Electrical Installation......................................................................................................................8
2.6 Field Wiring...................................................................................................................................9
2.7 Remote Mounting Installation......................................................................................................11
2.7.1 Bridge Voltage Adjustment......................................................................................................11
2.8 Initial Start Up .............................................................................................................................12
3. Operation ............................................................................................................................................. 13
3.1 Programming Magnet Operating Instructions................................................................................13
3.2 Operator Interface ........................................................................................................................14
3.3 Normal Operation ........................................................................................................................16
3.4 Calibration Mode (AutoSpan).......................................................................................................16
3.4.1 AutoZero .................................................................................................................................16
3.4.2 AutoSpan.................................................................................................................................17
3.5 Program Mode .............................................................................................................................18
3.5.1 View Sensor Status..................................................................................................................19
3.5.2 Set AutoSpan Level .................................................................................................................21
3.5.3 Set Gas Factor.......................................................................................................................... 21
3.5.4 Set Cal Factor ..........................................................................................................................23
3.5.5 Set Bridge Voltage...................................................................................................................23
3.5.6 Signal Output Check................................................................................................................ 24
3.5.7 Restore Factory Defaults..........................................................................................................24
3.5.8 Set Serial ID ............................................................................................................................25
3.5.9 Alarm 1 and 2 Settings.............................................................................................................26
3.5.10 Fault Settings.......................................................................................................................26
3.6 Program Features.........................................................................................................................27
3.6.1 Operational Features ................................................................................................................ 27
3.6.2 Fault Diagnostic/Failsafe Features............................................................................................28
4. RS-485 ModbusTMProtocol..................................................................................................................30
5. Service and Maintenance......................................................................................................................32
6. Troubleshooting Guide.........................................................................................................................34
7. Customer Support and Service Policy................................................................................................... 37
8. FP-624D Sensor Warranty....................................................................................................................38
9. Appendix..............................................................................................................................................39
9.1 Specifications...............................................................................................................................39
9.2 Spare Parts, Sensor Accessories, Calibration Equipment...............................................................41
9.3 Revision Log................................................................................................................................ 42
FP-624D InstructionManual iii
Model FP-624D
Shipping Address:
4055 Technology Forest Blvd, Suite 100,
The Woodlands Texas 77381
List of Figures
Figure 1 Sensor Assembly Front View............................................................................................................ 1
Figure 2 Sensor Cell Construction .................................................................................................................. 2
Figure 3 Wheatstone Bridge ........................................................................................................................... 2
Figure 4 Response Curves.............................................................................................................................. 3
Figure 5 Circuit Functional Block Diagram .................................................................................................... 3
Figure 6 Transmitter Module.......................................................................................................................... 4
Figure 7 Field Replaceable Combustible Gas Sensor....................................................................................... 4
Figure 8 Base Connector Board ...................................................................................................................... 5
Figure 9 Typical Outline and Mounting Dimensions....................................................................................... 8
Figure 10 Typical Installation......................................................................................................................... 9
Figure 11 Sensor Connector PCB ..................................................................................................................10
Figure 12 Remote Sensor Wiring Diagram.....................................................................................................11
Figure 13 Magnetic Programming Tool .........................................................................................................13
Figure 14 Magnetic Programming Switches...................................................................................................13
Figure 15 FP-624D Software Flowchart.........................................................................................................15
Figure 16 Replaceable Combustible Gas Sensor ...........................................................................................34
Figure 17 Plug-in Sensor (Bottom View).......................................................................................................34
List of Tables
Table 1 Wire Gauge vs. Distance...................................................................................................................10
Table 2 Gas/Cal Factors.................................................................................................................................22
Table 3 Modbus Registers .............................................................................................................................30
Table 4 Notation Text String Description.......................................................................................................31
FP-624D InstructionManual iv
Phone: 888.367.4286, 281.367.4100 • Fax: 281.292.2860 • www.detcon.com • sales@detcon.com
Mailing Address: P.O. Box 8067, The Woodlands Texas 77387-8067
Model FP-624D
1. Introduction
1.1 Description
Detcon Model FP-624D combustible gas sensors are non-intrusive “Smart” sensors designed to detect and
monitor combustible gases in air. Range of detection is 0-100% LEL (Lower Explosive Limit). The sensor
features an LED display of current reading, fault, and calibration status. The sensor is equipped with standard
analog 4-20mA, ModbusTMRTU output, and 3 relay contact outputs. A primary feature of the sensor is its
method of automatic calibration, which guides the user through each step via fully scripted instructions
displayed on the LED display.
The microprocessor-supervised electronics are packaged as a plug-in replaceable Transmitter Module that is
housed in an explosion proof junction box. The Transmitter Module includes a four character alpha/numeric
LED used to display sensor readings, and the sensor’s menu driven features when the hand-held programming
magnet is used.
PGM 1
MODEL FP-624DHOUSTON,TEXAS
TM
MicroSafe LEL GasSensor
ALM ALM
FLT 1 2 CAL
PGM 2
Figure 1 Sensor Assembly Front View
Catalytic Bead (Pellistor) Sensor Technology
The sensor technology is a poison-resistant catalytic bead type. Catalytic bead sensors show a strong response
to a long list of combustible gases. The sensor is supplied as a matched-pair of detector elements mounted in a
plug-in replaceable module. One bead is a catalytically active detector and the other is a non-active reference
detector. Each detector consists of a fine platinum wire coil embedded in aluminum oxide. A catalytic
mixture is applied to the active detector while the reference detector is treated so that oxidation of the gas does
not occur. The technique is referred to as non-selective and may be used to monitor most any combustible gas.
Detcon catalytic bead sensors are specifically designed to be resistant to poisons such as sulfides, chlorides,
and silicones. The sensors are characteristically stable and capable of providing reliable performance for
periods exceeding 5 years in most industrial environments.
FP-624D InstructionManual Rev. 1.2 Page 1 of 42
Model FP-624D
Platinum Wire
Catalyst
Construction
of Detector
Bead
Alumina Bead
Catalytic Beads
Main Housing Insert
Printed Circuit Board
Gold Plated Pins
Figure 2 Sensor Cell Construction
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
Compensator /
Reference Bead
Input
Voltage
Zero
Adjust
Detector /
Active Bead
Output
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.
FP-624D InstructionManual Rev. 1.2 Page 2 of 42
Figure 4 Response Curves
RS-4854-
20mA
Display
Control
Pre-Amp
Power Supply
1.2 Modular Mechanical Design
The Model FP-624D Sensor Assembly is completely modular and is made up of four parts:
1) FP-624D Plug-in Transmitter
2) Field Replaceable Combustible Gas Sensor
3) Connector PCB
4) Splash Guard
ModelFP-624D
FP-624D Plug-in Transmitter
The Plug-in Transmitter Module is a microprocessor-based package that plugs into the connector board located
in the explosion proof junction box. Circuit functions include extensive I/O circuit protection, sensor preamplifier, sensor temperature control, on-board power supplies, microprocessor, LED display, magnetic
programming switches, a linear 4-20mA DC output, and a Modbus RTU output. Magnetic program switches
located above and below the LED Display are activated via a hand-held magnetic programming tool, thus
allowing non-intrusive operator interface with the Transmitter Module. Calibration can be accomplished
without declassifying the area. Electrical classifications are Class I, Division 1, Groups B C D.
Analog 4-20mA Out
Plug-In
Sensor
Element
Temperature
Micro-
Processor
Figure 5 Circuit Functional Block Diagram
I/O
Circuit
Protection
Relays Out
Modbus RTU
Power In
FP-624D Instruction Manual Rev. 1.2 Page 3 of 42
PGM 1
MODEL FP-624DHOUSTON,TEXAS
Model FP-624D
MicroSafe LEL Gas Sensor
TM
ALM ALM
FLT 1 2 CAL
PGM 2
Figure 6 Transmitter Module
The transmitter module includes four LED status indicators (see Figure 3). These indicators are labeled FLT,
ALM1, ALM2 and CAL. The ALM1 and ALM2 LEDs are illuminated when the sensor is above the
corresponding alarm threshold. The FLT LED is illuminated when the sensor is in fault. The CAL LED is
illuminated solid when the sensor is completing an AutoZero or AutoSpan calibration. If the sensor is not
being calibrated, the CAL LED will flash each time the sensor answers a poll request from a Modbus
TM
master.
Field ReplaceableSensor
The Detcon combustible gas sensor is a field proven, replaceable type sensor. It can be accessed and replaced
in the field by removing the threaded insert from the lower housing and unplugging the replaceable sensor.
The Detcon combustible gas sensor has an infinite shelf life and is supported by a 2 year warranty.
Replaceable Sensor
Threaded Insert
O-ring
Main Housing
Figure 7 Field Replaceable Combustible Gas Sensor
NOTE: The Field Replaceable Combustible Gas Sensor housing is constructed from 316 Stainless Steel in
order to maximize corrosion resistance in harsh environments.
Base ConnectorPCB
The base connector board is mounted in the junction box. The connector board includes lug-less terminal
connections for incoming power, Modbus, and mA output, and connections for the Combustible Gas
Replaceable Sensor. Terminals for the 3 common and normally open/normally closed relay outputs are also
located on the base connector board.
FP-624D InstructionManual Rev. 1.2 Page 4 of 42
Model FP-624D
NOTE
: The relay outputs will not activate during the first 60 seconds after sensor power up.
Relays
Customer
Wiring
Wiringto
Figure 8 Base Connector Board
1.3 Relay Outputs
The FP-624D includes three 5A Form C relay outputs. Two of these relays are dedicated to alarm outputs, and
the third is used to indicate when the sensor is in fault. The common and normally closed contacts on the alarm
relays are connected when the gas concentration is below the alarm threshold. If the concentration exceeds the
alarm threshold for more than five seconds, then the common and normally open contacts will be connected.
The common and normally closed contacts on the fault relay are connected when the sensor is not in fault. If
the sensor experiences a fault condition for more than five seconds, then the common and normally open
contacts will be connected.
The common and either the normally open or the normally closed contacts from the alarm and fault relays are
connected to terminals on the base connector board. A jumper near each relay is used to select whether the
normally open or normally closed contact is connected to the terminal on the base connector board.
The relays can be configured to operate in Energized Mode. In this mode, the common and normally open
contacts are connected when the gas is below the alarm threshold (alarm relays) or is not in fault (fault relay).
This mode allows for fail-safe operation of the sensor. If the power to the sensor fails or the cable to the sensor
I/O is disconnected, then the common and normally open contacts will no longer be connected.
The alarm and fault relays can be configured as either latching or non-latching. In non-latching mode, the relay
is deactivated as soon as the sensor alarm or fault condition is cleared. In latching mode, the relay remains
active even after the alarm or fault condition has cleared. Once activated, the relay can only be deactivated by
swiping a magnetic programming tool above the PGM1 or PGM2 mark on the FP-624D face plate.
The alarm relays can be configured for ascending or descending mode. In ascending mode the relay will be
activated when the concentration is above the alarm threshold. This is the most common mode of operation for
the FP-624D. The alarm relays can also be activated in descending mode. In this mode, the alarm relays will
activate when the concentration is below the alarm threshold.
This allows the sensor cell to stabilize and begin outputting an accurate reading.
FP-624D InstructionManual Rev. 1.2 Page 5 of 42
Model FP-624D
NOTE:
Methane and Hydrogen are lighter than air. Most other combustible gases are
heavier
2. Installation
2.1 Operational Guidelines for Safe Use
1. Install sensor only in areas with classifications matching with those described on the approval label.
Follow all warnings listed on the label.
2. Ensure that the sensor is properly mounted in a vertical orientation with sensor facing down. Avoid
use of excessive Teflon Tape, or any type of non-conductive pipe thread coating on the NPT threaded
connection. All NPT connections should remain grounded to the junction box.
3. Use ¾” NPT plugs properly rated for hazardous locations to block any unused connections.
4. Removal of the Junction box cover or threaded sensor housing (612-820000-000) violates the Ex
Proof protection method and hence power must be removed from the sensor prior to its safe removal.
5. Ensure that the threaded insert and plug-in sensor are installed during operation. The threaded insert
should be secured tightly to the sensor housing. Removal of the threaded insert violates the Ex Proof
protection method and hence power must be removed from the sensor prior to its safe removal.
6. Proper precautions should be taken during installation and maintenance to avoid the build-up of static
charge on the plastic components of the sensor. These include the splashguard and splashguard
adapter.
7. Do not operate the sensor outside of the stated operating temperature limits.
8. Do not operate the sensor outside the stated operating limits for voltage supply.
2.2 Sensor Placement
Selection of sensor location is critical to the overall safe performance of the product. Six 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) Maintenance access
(6) Additional Placement Considerations
Density
Placement of sensors relative to the density of the target gas is such that sensors for the detection of heavier
than air gases should be located within 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.
than air. Compare the molecular weight, density, or specific gravity of the target gas(es) with
that of air to determine appropriate placement.
FP-624D InstructionManual Rev. 1.2 Page 6 of 42
Model FP-624D
NOTE:
In all installations the gas sensor should point straight down (refer to
Figure
10
).
Leak Sources
The most probable leak sources within an industrial process include flanges, valves, and tubing connections 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.
Ventilation
Normal ventilation or prevailing wind conditions can dictate efficient location of gas sensors in a manner
where the migration of gas clouds is quickly detected.
Personnel Exposure
The undetected migration of gas clouds should not be allowed to approach concentrated personnel areas such
as control rooms, maintenance or warehouse buildings. A more general approach toward selecting sensor
location is combining leak source and perimeter protection in the best possible configuration.
Maintenance Access
Consideration should be given to providing easy access for maintenance personnel. Consideration should also
be given to the consequences of close proximity to contaminants that may foul the sensor prematurely.
Improper sensor orientation may result in false readings and permanent sensor damage.
Additional Placement Considerations
The sensor should not be positioned where it maybe sprayed or coated with surface contaminating substances.
Painting sensor assemblies is prohibited.
Although the sensor is designed to be RFI resistant, it should not be mounted in close proximity to highpowered radio transmitters or similar RFI generating equipment.
When possible mount in an area void of high wind, accumulating dust, rain, or splashing from hose spray,
direct steam releases, and continuous vibration. If the sensor cannot be mounted away from these conditions
then make sure the Detcon Harsh Location Dust Guard accessory is used.
Do not mount in locations where temperatures will exceed the operating temperature limits of the sensor.
Where direct sunlight leads to exceeding the high temperature-operating limit, use a sunshade to help reduce
temperature.
2.3 Sensor Contaminants and Interference
Detcon combustible gas sensors may be adversely affected by exposure to certain airborne substances. Loss of
sensitivity or corrosion may be gradual if such materials are present in sufficient concentrations.
The performance of the detector elements may be temporarily impaired during operation in the presence of
substances described as inhibitors. Inhibitors are usually volatile substances containing halogen compounds.
Inhibitors include halide compounds such as Cl2, ClO2, F2, HF, HCl, Br2, vinyl chloride, and methyl chloride.
Inhibition is typically a temporary effect and the detectors generally recover after short periods of operation
back in clean air.
Some background gases may act as poisoning agents and have a more damaging effect on the sensor.
Although the sensor is designed to be poison resistant, it does have physical limits. Poisoning gases deactivate
the active detector’s catalytic ability and cause a permanent reduction in the span sensitivity. Examples of
FP-624D InstructionManual Rev. 1.2 Page 7 of 42
Model FP-624D
NOTE:
Do not use Teflon Tape or any other
type of Pipe Thread material on the ¾” threads
typical poisons are: silicone oils and greases, siloxanes (HMDS), H2S, anti-knock petrol additives, and
phosphate esters. Activated carbon filters can be used to provide additional protection from poisoning in most
cases.
The presence of such inhibitors and poisons in an area does not preclude the use of this sensor technology,
although it is likely that the sensor lifetime will be shorter as a result. Use of this sensor in these environments
may require more frequent calibration checks to ensure safe system performance.
2.4 Mounting Installation
The FP-624D should be vertically oriented so that the sensor points straight downward. The explosion-proof
enclosure or junction box would then typically be mounted on a wall or pole (See Figure 9). Detcon provides
a selection of standard junction boxes in both Aluminum and Stainless Steel.
unless the unit is mounted in a severe or harsh environment. Metal-on-metal contact must be
maintained to provide a solid electrical ground path. If Teflon Tape is used the Sensor must be
externally grounded using a ground strap.
When mounting on a pole, secure the Junction Box to a suitable mounting plate and attach the mounting plate
to the pole using U-Bolts. (Pole-Mounting brackets for Detcon Junction Box’s are available separately.)
6.985"
1
" mounting holes
4
6.125"
5.5"
2.1"
2"
0.5"
3
NPT Ports
4
5.25"
8-32 tapped
ground point
LEL Sensor
Splash Guard
Figure 9 Typical Outline and Mounting Dimensions
4.6"
Wall (or other
mounting surface)
2.5 Electrical Installation
The Sensor Assembly should be installed in accordance with local electrical codes. The sensor assemblies are
CSA/NRTL approved (US and Canada) for Class I, Division 1, Groups B C D area classifications.
FP-624D InstructionManual Rev. 1.2 Page 8 of 42
Model FP-624D
NOTE:
If a conduit run exits the secondary port, repeat the installation techniqu
e shown in
NOTE:
A conduit seal is typically required to be located within 18" of the J
-
Box and Sensor
NOTE:
The Detcon Warranty does not cover water damage resulting from water leaking into
NOTE:
Any unused ports should be blocked with suitable ¾” male NPT plugs. Detcon
Proper electrical installation of the gas sensor is critical for conformance to Electrical Codes and to avoid
damage due to water leakage. Refer to Figure 10 and Figure 11 for proper electrical installation.
Figure 10.
In Figure 10, the drain allows H2O condensation inside the conduit run to safely drain away from the sensor
assembly. The electrical seal fitting is required to meet the National Electrical Code per NEC Article 500-3d
(or Canadian Electrical Code Handbook Part 1 Section 18-154). Requirements for locations of electrical seals
are covered under NEC Article 501-5. Electrical seals also act as a secondary seal to prevent water from
entering the wiring terminal enclosure. However, they are not designed to provide an absolute watertight seal,
especially when used in the vertical orientation.
Assembly. Crouse Hinds type EYS2, EYD2 or equivalent are suitable for this purpose.
the enclosure.
Conduit
"T"
Drain
EYS Seal Fitting
PGM 1
MODEL TP-624DHOUSTON,TEXAS
TM
MicroSafe H2S Gas Sensor
ALM ALM
FLT 1 2 CAL
PGM 2
Figure 10 Typical Installation
Supplies one ¾” NPT male plug with each J-box enclosure. If connections are other than ¾”
NPT, use an appropriate male plug of like construction material.
2.6 Field Wiring
Detcon Model FP-624D combustible gas sensor assemblies require up to five conductor connections between
power supplies and host electronic controller. Wiring designations are DC+, DC-, MA (sensor signal), Modbus
A and Modbus B. If the MA signal is not needed, its terminal may be left unconnected. A 250 ohm load
resistor is needed on the 4-20 mA line when it is not being used. The maximum wire length between sensor
FP-624D InstructionManual Rev. 1.2 Page 9 of 42
ModelFP-624D
Over
-
Current
22
0.723mm
700
2080
3A200.812mm
1120
3350
5A181.024mm
1750
5250
7A161.291mm
2800
8400
10A141.628mm
4480
13,440
20A
NOTE 1:
Wiring table is based on stranded tinned copper wire and is designed to serve as a
NOTE 2:
Shielded cable is required for installations where cable trays or conduit runs include
NOTE 3:
The supply of power shou
ld be from an isolated source with over
-
current protection
NOTE 4:
A 250 ohm load resistor is need
ed on the 4
-
20 mA line when it is not being used.
and 24VDC source is shown in the Table below. The maximum wire size for termination in the Junction Box
is 14 AWG.
Table 1 Wire Gauge vs. Distance
AWG Wire Dia. Meters Feet
reference only.
high voltage lines or other possible sources of induced interference. Separate conduit runs are
highly recommended in these cases.
as stipulated in Table 1 Wire Gauge vs. Distance.
Terminal Connections
CAUTION: Do not apply System power to the sensor until all wiring is properly terminated. Refer
to Section 2.8 Initial Start Up
Protection
Alarm 2
Black
Blue
Yellow
Alarm 1
Wiringto
LEL Sensor
Fault
Customer
Wiring
Power(+ -)
4-20mA
RS-485 (A,B)
White
Figure 11 Sensor Connector PCB
a) Remove the junction box cover and unplug the Transmitter Module. Identify the terminal blocks for
customer wire connections.
FP-624D Instruction Manual Rev. 1.2 Page 10 of 42
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