Detcon FP-624D-HT User Manual

INSTRUCTION MANUAL

DETCON, Inc.

April 23, 2012

• Document #

3458

• Revision

1.1

Detcon Model FP-624D-HT

FP-624D-HT Combustible Gas Sensor

(0-100% LEL)

4055 Technology Forest Blvd, Suite 100,

The Woodlands, Texas 77381

Ph.281.367.4100 / Fax [phone]

www.detcon.com

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Model FP-624D-HT

FP-624D-HT Instruction Manual ii

Model FP-624D-HT

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......................................................................................................................9

2.6 Field Wiring.................................................................................................................................10

2.7 Remote Mounting Installation ......................................................................................................11

2.7.1 Bridge Voltage Adjustment......................................................................................................12

2.8 Initial Start Up ............................................................................................................................. 12

3. Operation .............................................................................................................................................14

3.1 Programming Magnet Operating Instructions................................................................................ 14

3.2 Operator Interface........................................................................................................................15

3.3 Normal Operation ........................................................................................................................ 17

3.4 Calibration Mode (AutoSpan)....................................................................................................... 17

3.4.1 AutoZero .................................................................................................................................17

3.4.2 AutoSpan................................................................................................................................. 18

3.5 Program Mode .............................................................................................................................19

3.5.1 View Sensor Status ..................................................................................................................20

3.5.2 Set AutoSpan Level ................................................................................................................. 22

3.5.3 Set Gas Factor..........................................................................................................................22

3.5.4 Set Cal Factor .......................................................................................................................... 24

3.5.5 Set Bridge Voltage...................................................................................................................24

3.5.6 Signal Output Check................................................................................................................25

3.5.7 Restore Factory Defaults..........................................................................................................25

3.5.8 Set Serial ID ............................................................................................................................ 26

3.5.9 Alarm 1 and 2 Settings............................................................................................................. 27

3.5.10 Fault Settings.......................................................................................................................27

3.6 Program Features .........................................................................................................................28

3.6.1 Operational Features................................................................................................................ 28

3.6.2 Fault Diagnostic/Failsafe Features............................................................................................ 29

4. RS-485 ModbusTMProtocol..................................................................................................................31

5. Service and Maintenance...................................................................................................................... 33

6. Troubleshooting Guide.........................................................................................................................35

7. Customer Support and Service Policy...................................................................................................38

8. FP-624D-HT Sensor Warranty.............................................................................................................. 39

9. Appendix.............................................................................................................................................. 40

9.1 Specifications...............................................................................................................................40

9.2 Spare Parts, Sensor Accessories, Calibration Equipment............................................................... 42

9.3 Revision Log................................................................................................................................ 43

FP-624D-HT Instruction Manual iii

Model FP-624D-HT

Shipping Address: 4055 Technology Forest, 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 Base Connector Board...................................................................................................................... 4

Figure 8 Typical Outline and Mounting Dimensions....................................................................................... 9

Figure 9 Typical Installation..........................................................................................................................10

Figure 10 Sensor Connector PCB ..................................................................................................................11

Figure 11 Remote Sensor Wiring Diagram.....................................................................................................12

Figure 12 Magnetic Programming Tool .........................................................................................................14

Figure 13 Magnetic Programming Switches...................................................................................................14

Figure 14 FP-624D-HT Software Flowchart ..................................................................................................16

Figure 15 Replaceable High Temperature Combustible Gas Sensor ..............................................................35

List of Tables

Table 1 Wire Gauge vs. Distance...................................................................................................................10

Table 2 Gas/Cal Factors.................................................................................................................................23

Table 3 Modbus Registers .............................................................................................................................31

Table 4 Notation Text String Description.......................................................................................................32

Phone: [phone] • Fax: [phone] • www.detcon.com • [e-mail]

FP-624D-HT Instruction Manual iv

Mailing Address: P.O. Box 8067, The Woodlands Texas 77387-8067

Model FP-624D-HT

1. Introduction

1.1 Description

Detcon Model FP-624D-HT High Temperature 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-624HOUSTON,TEXAS

TM

MicroSafe LEL Ga s Sensor

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-HT Instruction Manual Rev. 1.1 Page 1 of 44

Model FP-624D-HT

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-HT Instruction Manual Rev. 1.1 Page 2 of 44

Figure 4 Response Curves

RS-4854-

20mA

Display

Control

Pre-Amp

Power Supply

1.2 Modular Mechanical Design

The Model FP-624D-HT Sensor Assembly is completely modular and is made up of four parts:

1) FP-624D-HT Plug-in Transmitter

2) Field Replaceable High Temperature combustible gas sensor

3) Connector PCB

4) Splash Guard

ModelFP-624D-HT

FP-624D-HT 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-HT Instruction Manual Rev. 1.1 Page 3 of 44

PGM 1

MODEL FP-624DHOUSTON,TEXAS

Model FP-624D-HT

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.

Base Connector PCB

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.

Relays

Customer

Wiring

Wiringto

Figure 7 Base Connector Board

FP-624D-HT Instruction Manual Rev. 1.1 Page 4 of 44

Model FP-624D-HT

NOTE

: The relay outputs will not activate during the first 60 seconds after sensor power up.

1.3 Relay Outputs

The FP-624D-HT 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-HT 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-HT. 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-HT Instruction Manual Rev. 1.1 Page 5 of 44

Model FP-624D-HT

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 High Temperature senor violates the Ex Proof protection
method and hence power must be removed from the sensor prior to its safe removal.

5. 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.

6. Do not operate the sensor outside of the stated operating temperature limits.

7. 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

FP-624D-HT Instruction Manual Rev. 1.1 Page 6 of 44

Model FP-624D-HT

NOTE:

Methane and Hydrogen are lighter than air. Most other combustible gases are heavier

NOTE:

In all installations the gas sensor should point straight down (refer to

Figure

9

).

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.

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 may be 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

FP-624D-HT Instruction Manual Rev. 1.1 Page 7 of 44

Model FP-624D-HT

NOTE:

Do not u

se Teflon Tape or any other type of Pipe Thread material on the ¾” threads

Detcon High Temperature 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
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-HT should be vertically oriented so that the sensor points straight downward. The explosion­proof enclosure or junction box would then typically be mounted on a wall or pole (See Figure 8). 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.)

FP-624D-HT Instruction Manual Rev. 1.1 Page 8 of 44

Model FP-624D-HT

NOTE:

If a conduit run exits the secondary port, repeat the installation technique 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

1

" mounting holes

4

0.5"

6.1"

5.5"

2.1"

2"

3

NPT Ports

4

5.825"

High Temperature
LEL Sensor

Splash Guard

4.65"

External Ground Screw
8-32 x 5/16" binding
head screw

Wall (or other

mounting surface)

Figure 8 Typical Outline and Mounting Dimensions

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.

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 9 and Figure 8 for proper electrical installation.

Figure 9.

In Figure 9, 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.

FP-624D-HT Instruction Manual Rev. 1.1 Page 9 of 44

NOTE:

Any unused ports should be blocked with suitable ¾” male NPT plugs. Detcon

Over

-

Current

22

0.723mm

700

2080

3A

20

0.812mm

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 needed on the 4

-

20 mA line when it is not being used.

Conduit

Model FP-624D-HT

"T"

Drain

EYS Seal Fitting

Figure 9 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-HT High Temperature 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 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

Protection

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.

FP-624D-HT Instruction Manual Rev. 1.1 Page 10 of 44

Terminal Connections

NOTE

: A 6

-

32 or 8

-

32 threaded exterior ground point is provided on most junction boxes for

CAUTION: Do not apply System power to the sensor until all wiring is properly terminated. Refer

to Section 2.8 Initial Start Up

Customer

Wiring

Power(+ -)
4-20mA

RS-485 (A,B)

ModelFP-624D-HT

Alarm 2

Black

Blue

Yellow

Alarm 1

Wiringto

LEL Sensor

Fault

White

Figure 10 Sensor Connector PCB

a) Remove the junction box cover and unplug the Transmitter Module. Identify the terminal blocks for

customer wire connections.

b) Observing correct polarity, terminate the field wiring (DC+, DC-, MA, A, and B) to the sensor assembly

wiring in accordance with the detail shown in Figure 10

c) Trim all exposed wire leads if they are not permanently landed in the terminal block.

d) Plug the Transmitter Module into the connector PCB and replace the junction box cover.

an external ground. If the Sensor Assembly is not mechanically grounded, an external ground
strap must be used to ensure that the sensor is electrically grounded.

2.7 Remote Mounting Installation

Some sensor mounting applications require that the gas sensor head be remotely mounted away from the
sensor transmitter. This is usually true in instances where the gas sensor head must be mounted in a location
that is difficult to access. Such a location creates problems for maintenance and calibration activities. Detcon
provides the FP-624D-HT sensor in a remote-mount configuration in which the sensor (Model FP-624D-HT­RS) and the transmitter (Model FP-624D-HT-RT) are provided in their own condulet housing and are
interfaced together with a three conductor cable. There is a limit 0.5 ohm maximum resistance drop per wire
over the separation distance.

FP-624D-HT Instruction Manual Rev. 1.1 Page 11 of 44