Model FP-424C
detcon inc.
4-20 mA Combustible Gas Sensor (0-100% LEL)
Operator’s Installation & Instruction Manual
May 18, 2010 • Document #2243T • Version 3.8
CAUTION: FOR SAFETY REASONS THIS EQUIPMENT MUST BE OPERATED
AND SERVICED BY QUALIFIED PERSONNEL ONLY. READ AND UNDERSTAND
INSTRUCTION MANUAL COMPLETELY BEFORE OPERATING OR SERVICING.
ATTENTION: POUR DES RAISONS DE SECURITE, CET EQUIPEMENT DOIT ETRE
UTILISE ENTRETENU ET REPARE UNIQUEMENT PAR UN PERSONNEL QUALIFIE. ETUDIER LE MANUEL D'INSTRUCTIONS EN ENTIER AVANT D'UTILISER,
D'ENTRETENIR OU DE REPARER L'EQUIPEMENT.
phone 888-367-4286, 281-367-4100 • fax 281-292-2860 • www.detcon.com • sales@detcon.com
Table of Contents
1.0 Description
2.0 Principle of Operation
3.0 Application
4.0 Specifications
5.0 Installation
6.0 Start-up
7.0 Calibration
8.0 Fault Supervision
9.0 Trouble Shooting Guide
10.0 Spare Parts List
11.0 Warranty
12.0 Service Policy
Detcon Model FP-424C Combustible Gas Sensor PG.2
1.0 DESCRIPTION
Alumina Bead
Platinum Wire
Catalyst
Construction of
Detector Bead
Sintered Stainless Steel Can
Header
Gold Plated Pins
Beads
BRDG
FP-424C
+
% LEL
4
-
20 mA DC
T
E
X
A
S
H
O
U
S
T
O
N
VOLT
detcon inc.
ZERO
BRIDGE
SIGNAL
FLT
DET
FLT
FINE
COARSE
Detcon Model FP-424C combustible gas detection sensors are designed to monitor ambient air for combustible hydrocarbons in the lower explosive limit range (0-100% LEL). The sensor assembly consists of a
plug in replaceable matched pair of catalytic beads mounted in a stainless steel housing, a 12-28 VDC 4-20
A DC control transmitter, an explosion proof junction box, and a machine fitted rain shield.
m
1.1 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.
1.2 Control Transmitter Circuit
The control transmitter is a remote mounted electronic circuit designed and packaged as a plug-in module.
The transmitter assembly consists of several circuit functions: input power conditioning, sensor heater control, sensor signal conditioning, sensor fault supervision, and fault LEDs. A metallic face plate with pull
ring identifies test points and calibration adjustments. The plug-in module design supports easy field level
maintenance and repair. The mating plug is gold plated for maximum resistance to corrosion.
1.3 Terminal Connector Board
The terminal 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 and terminals
that do not require lugs for all field wiring.
Detcon Model FP-424C Combustible Gas Sensor PG.3
1.4 Explosion Proof Enclosure
BLUE
YELLOWMA
24VDC
To Controller
Te r mi n a l s
BLACK
WHITE
Sensor
–
+
4-20MA
The transmitter electronics are packaged in a cast aluminum explosion proof enclosure and given a baked
epoxy paint finish. The explosion proof enclosure has 3/4” NPT female entry ports. The enclosure is fitted
with a threaded cover. Electrical classification is Class I, Div. 1; Groups B, C, D.
1.5 Rain Shield
The machine fitted rain shield is designed to help prevent obstruction of the sintered stainless steel flame
arrestor as a result of liquid or solid contact. Material of construction is Dupont Delrin.
2.0 PRINCIPLE OF OPERATION
In operation, FP-424C series sensor assemblies are installed in industrial areas where early detection of gas
leaks is most likely. The sensor is powered by 12-28 VDC. Air and gas diffuses through the porous sintered
flame arrestor and contacts the active and compensating detector elements. Electronically, the detector elements form part of a bridge circuit as shown below. The balance potentiometer is used to set the output of
the bridge circuit referenced to zero gas. As the active detector element reacts to the presence of combustible gas and the compensating element does not react, the bridge voltage output changes. This voltage
change is conditioned by the transmitter circuit to provide for a linear 4-20 mA DC signal output. As combustible gas dissipates and the sensor is returned to a zero gas environment the bridge circuit returns to a
balanced condition. In application, sensor operation is a continuous reading detection/monitoring method.
Detcon Model FP-424C Combustible Gas Sensor PG.4
2.1 Characteristics
RESPONSE CURVE
% 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
2
.7V
Z
ero
Set
P
ot
O
utput
Detector/Active
C
ompensator/Reference
R
1
R
2
The detector elements maintain good sensitivity to combustible hydrocarbons 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.
Note: If it is suspected that the sensor has been poisoned its sensitivity should be verified by recalibrating.
3.0 APPLICATION
Model FP-424C 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.
3.1 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.
One of the characteristics of the catalytic type combustible gas detectors is their almost universal response
to virtually any and all combustible gases. The partial list of detectable gases that appears in our literature
includes a list of response K-Factors. These factors are used to determine cross calibration references when
detectors are calibrated with other than the target gas. They may also be used to calculate expected readings when a gas other than the target and calibration substance occurs in the area of the sensor. The follow-
3.2 Response to Different Gases
ing formulas apply when converting to either of these occurrences.
Detcon Model FP-424C Combustible Gas Sensor PG.5
When calibrating with one gas (Cal Gas) and scale sensitivity is required for a different gas (Target Gas) use
Methylethylketone
Cyclohexane
Benzene
Hydrogen Sulphide
Methyl n-propylketone
Toluene
2,3-Dimethylpentane
Triethylamine
2,2-Dimethylpropane
Ethylcyclopentane
Aniline
m-Xylene
p-Xylene
n-Heptane
n-Butyric Acid
n-Octane
n-Hexane
o-Xylene
Ethyl Benzene
n-Butyl Alcohol
Naphthalene
Naptha
Decane
n-Amyl Alcohol
iso-Butyl Benzene
n-Butyl Benzene
n-Nonane
Biphenyl
Carbon Disulphide
2.42
2.43
2.45
2.45
2.46
2.47
2.51
2.51
2.52
2.52
2.54
2.55
2.55
2.59
2.63
2.67
2.71
2.79
2.80
2.91
2.94
3.03
3.05
3.06
3.12
3.18
3.18
4.00
5.65
Ethyleneoxide
Ethyl Acetate
Methylpropionate
Propylene
Alkyl Alcohol
trans-Butene-2
Methyl Acetate
Diethylamine
cis-Butene-2
Trimethylamine
n-Propylamine
Hydrogencyanide
n-Propyl Alcohol
iso-Pentane
Diethyl Ether
Acetic Anhydride
n-Pentane
Propyleneoxide
Butene-1
Hydrazine
1,4-Dioxane
Ethyl Formate
Methylcyclohexane
Methylethylether
iso-Propylether
Dimethylsulphide
Vinyl Chloride
Vinylethylether
Propyne
1.93
1.95
1.95
1.95
1.96
1.97
2.01
2.05
2.06
2.06
2.07
2.09
2.12
2.15
2.16
2.17
2.18
2.18
2.20
2.22
2.24
2.26
2.26
2.27
2.29
2.30
2.32
2.38
2.40
Ammonia
Methane
Carbon Oxysulphide
Cyanogen
Methyl Alcohol
Methylamine
Hydrogen
Carbon Monoxide
tert-Buty-alcohol
Ethyl Alcohol
Ethylene
Ethane
Methyl Formate
Cyclopropane
Dimethyl Ether
Methylmercaptan
Acetaldehyde
Butane
Nitromethane
Dimethylamine
Acetylene
Ethylmercaptan
1,3-Butadiene
Propane
Acetic Acid
iso-Butyl Alcohol
Ethylamine
Acetone
iso-Butane
0.79
1.00
1.07
1.12
1.16
1.29
1.30
1.32
1.34
1.37
1.41
1.47
1.49
1.60
1.60
1.64
1.66
1.71
1.72
1.73
1.76
1.78
1.79
1.81
1.84
1.89
1.90
1.93
1.93
Gas KGas KGas K
TABLE 1b (numerical listing)
Dimethyl Ether
M
ethylethylether
Methylethylketone
Methyl Formate
Methylmercaptan
Methylpropionate
Methyl n-propylketone
Naptha
Naphthalene
Nitromethane
n-Nonane
n-Octane
n-Pentane
i
so-Pentane
P
ropane
n-Propyl Alcohol
n-Propylamine
Propylene
Propyleneoxide
iso-Propylether
Propyne
Toluene
Triethylamine
Trimethylamine
Vinyl Chloride
Vinylethylether
o-Xylene
m-Xylene
p-Xylene
1.60
2
.27
2.42
1.49
1.64
1.95
2.46
3.03
2.94
1.72
3.18
2.67
2.18
2
.15
1
.81
2.12
2.07
1.95
2.18
2.29
2.40
2.47
2.51
2.06
2.32
2.38
2.79
2.55
2.55
Decane
D
iethylamine
Dimethylamine
2,3-Dimethylpentane
2,2-Dimethylpropane
Dimethylsulphide
1,4-Dioxane
Ethane
Ethyl Acetate
Ethyl Alcohol
Ethylamine
Ethyl Benzene
Ethylcyclopentane
E
thylene
E
thyleneoxide
Diethyl Ether
Ethyl Formate
Ethylmercaptan
n-Heptane
n-Hexane
Hydrazine
Hydrogencyanide
Hydrogen
Hydrogen Sulphide
Methane
Methyl Acetate
Methyl Alcohol
Methylamine
Methylcyclohexane
3
.05
2.05
1.73
2.51
2.52
2
.30
2.24
1.47
1
.95
1
.37
1.90
2.80
2.52
1.41
1
.93
2.16
2.26
1.78
2.59
2.71
2.22
2.09
1.30
2.45
1.00
2.01
1.16
1.29
2.26
Acetaldehyde
A
cetic Acid
Acetic Anhydride
Acetone
Acetylene
Alkyl Alcohol
Ammonia
n-Amyl Alcohol
Aniline
Benzene
Biphenyl
1,3-Butadiene
Butane
i
so-Butane
B
utene-1
cis-Butene-2
trans-Butene-2
n-Butyl Alcohol
iso-Butyl Alcohol
tert-Buty-alcohol
n-Butyl Benzene
iso-Butyl Benzene
n-Butyric Acid
Carbon Disulphide
Carbon Monoxide
Carbon Oxysulphide
Cyanogen
Cyclohexane
Cyclopropane
1.66
1
.84
2.17
1.93
1.76
1.96
0.79
3.06
2.54
2.45
4.00
1.79
1.71
1
.93
2
.20
2.06
1.97
2.91
1.89
1.34
3.18
3.12
2.63
5.65
1.32
1.07
1.12
2.43
1.60
Gas KGas
K
Gas K
TABLE 1a (alphabetical listing)
he following calculation to determine calibration adjustment requirements: Target Gas K-Factor/Cal Gas
t
K-Factor x Cal Gas concentration = Required adjustment level. For example, when calibrating with 50%
LEL methane when propane is the target gas: 1.81/1.00 x .5 = 90.5%. The sensor response is lower to
propane than it is to methane. We therefore need to adjust scale sensitivity higher when methane is used as
the Cal Gas.
When a sensor has been calibrated with one gas and another gas occurs in the area of that sensor, the scale
response is calculated as: Cal Gas K-Factor/Target Gas K-Factor. For example, when a sensor has been calibrated with methane and propane occurs in the area: 1.00/1.81 = 55%. If 40% LEL propane occurred the
sensor output would equal 22.0%.
In all cases remember that these K-Factor ratios are theoretical. Actual response may vary from sensor to
sensor. Always use the Target Gas as the Cal Gas when possible.
Detcon Model FP-424C Combustible Gas Sensor PG.6
4.0 SPECIFICATIONS
Method of Detection
Catalytic detector diffusion/adsorption
easurement Range
M
0-100% LEL (lower explosive limit)
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 +167° F; -40° to +75°C
Operating Humidity Range
0-100% RH (non-condensing)
Output
Linear 4-20 mA DC
Input Voltage
11.5-28 VDC
Power Consumption (maximum)
< 2.1 watts @ 24 VDC
Electrical Classification
Explosion Proof; Class I, Div. 1; Groups B, C, D
Safety Approvals
CSA/NRTL (US OSHA Certified)
Warranty
Sensor: 2 year conditional
Transmitter: 2 year
Field Wiring
3 conductor; max 10 ohms single conductor resistance
Max Ohms Between Sensor and Transmitter (in applications where sensor head is remotely mounted)
1/2 ohm
5.0 INSTALLATION
Optimum performance of ambient air/gas sensor devices is directly relative to proper application and
installation practice.
5.1 Field Wiring Table
Detcon Model FP-424C wiring consists of three conductors: + (+24VDC power), – (DC common), and MA
(4-20 mA DC signal output referenced to DC common). Maximum single conductor resistance between
sensor and controller is 10 ohms. Maximum wire size for termination in the sensor assembly terminal connector board is 14 gauge. Note the wiring table below.
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 volt-
Note 3: The supply of power must be from an isolating source with over-current protection as follows:
AWG Over-current Protection AWG Over-current Protection
22 3A 16 10A
20 5A 14 20A
18 7A 12 25A
This wiring table is based on stranded tinned copper wire and is designed to serve as a reference only.
age lines or other sources of induced interference.
Detcon Model FP-424C Combustible Gas Sensor PG.7
5.2 Remote Mount Considerations
EYS
Seal
Fitting
Drain
“T”
Plug any unused ports.
f the application requires that the sensor head be remotely mounted away from the transmitter, maximum
I
line resistance should be 1/2 ohm. Use the wiring table below.
AWG Maximum Length (feet)
20 50
18 75
16 125
14 175
5.3 Sensor Location
Selection of physical 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) Maintenance access
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 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. Give consideration to easy access by maintenance personnel as well
as the consequences of close proximity to contaminants that may foul the sensor prematurely.
Leak Sources - 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 and
applicable thought toward selecting sensor location is combining leak source and perimeter protection in
the best possible configuration.
Note: In all installations, the sensor in stainless steel housing points down relative to grade (Fig. 1).
Improper sensor orientation will result in false reading and permanent sensor damage.
Figure #1
Detcon Model FP-424C Combustible Gas Sensor PG.8
5.4 Local Electrical Codes
4 3/4"
3/4" NPT
1/4" Dia.
Mounting Holes
7 1/4"
6 1/8"
5 1/2"
3/4" NPT
Rainshield/
Splashguard
2"
2 1/8"
BLUE
YELLOW
MA
24VDC
To Controller
Te rm i na l s
BLACK
WHITE
Sensor
–
+
4-20MA
ensor and transmitter assemblies should be installed in accordance with all local electrical codes. Use
S
appropriate conduit seals.
Drains are required at the bottom of vertical conduit runs. The sensor assemblies
are designed to meet NEC and CSA requirements for Class I; Groups B, C, D; Div. 1 environments.
Note: An appropriate conduit seal must be located within 18" of the sensor assembly. Crouse Hinds type
EYS2, EYD2 or equivalent are suitable for this purpose.
5.5 Installation Procedure
Note: See section 5.6 for special information on remote mounting applications in which the sensor (Model
FP-424C-RS) is remotely mounted away from the transmitter (Model FP-424C-RT).
a) Remove the junction box cover and un-plug the control transmitter by pulling it out via the pull ring.
b) Securely mount the sensor junction box in accordance with recommended practice. See dimensional
drawing (Fig. 2).
Figure #2
c) Terminate 3 conductor field wiring to the sensor terminal connector board observing correct polarity in
accordance with the detail shown in figure 3.
Figure #3
Detcon Model FP-424C Combustible Gas Sensor PG.9
d) Replace the plug-in transmitter module and the junction box cover.
1234
WHT
BLK
YEL
BLU
Install
Jumper
Remote Transmitter
FP-424C-RT
Remote Sensor
FP-424C-RS
Measure Bridge Voltage
From White (1) to Blue (4)
Target voltage is 2.7v
W
HT
B
LK
Y
EL
BLU
Plug unused port
with 3/4 NPT plug.
5.6 Remote Mounting Applications
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-424C sensor in a remote-mount configuration in which the sensor (Model FP-424CRS) and the transmitter (Model FP-424C-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
seperation distance.Ω
Reference figure 4 for wiring diagram. Also note the jumper that is required on the remote sensor terminal
Figure #4
connector board. Failure to install this jumper will cause a sensor fault condition.
Remote Mounting Configuration - Bridge Voltage Adjustment
When a sensor is remotely mounted away from the transmitter, consideration must be given to the lengths
of cable used and how it affects the sensor bridge voltage. Differing lengths of cables will have varying
amounts of resistance which will shift the sensor bridge voltage. Because of this, the bridge voltage will
need to be adjusted after initial power up. This adjustment is only required after initial installation and will
not be necessary thereafter, even in the event of replacement of the plug-in sensor. See section 6.1 for
instructions.
6.0 START UP
Upon completion of all mechanical mounting and termination of all field wiring, apply system power and
observe the following normal conditions:
a) Detcon electronic controller “Fault” LED is off.
b) A temporary upscale reading will occur as the sensor powers up.
6.1 Remote Mount Bridge Voltage Set
If the sensor has been installed using the remote mounting configuration as described in section 5.6, the
sensor bridge voltage must be adjusted after initial power up. If this is not the case skip this section and
proceed to Initial Operational Tests. Otherwise follow the steps below to set the sensor bridge voltage.
Detcon Model FP-424C Combustible Gas Sensor PG.10
aterial Requirements
BRDG
FP-424C
+
% LEL
4
-
20 mA DC
T
E
X
A
S
H
O
U
S
T
O
N
VOLT
detcon inc.
ZERO
BRIDGE
SIGNAL
FLT
DET
F
LT
FINE
COARSE
M
* Digital volt meter
* Jewelers type screwdriver
a) Declassify the area around the sensor.
b) Remove the junction box cover from the remote sensor enclosure (see figure 4).
c) Using the digital volt/ohm meter, measure the bridge voltage at the remote sensor terminal connector board
from the “White” terminal to the “Blue” terminal as shown in figure 4. Target voltage is 2.7 volts.
d) At the transmitter, adjust the “VOLT” potentiometer (see figure #5) to achieve a reading of 2.7 vdc
(±0.2v) at the remote sensor terminal connector board as described in item “c” above.
Figure #5
e) Replace the junction box cover on the remote sensor enclosure.
Bridge voltage set is complete. This procedure need only be done once after initial power up.
6.2 Initial Operational Tests
After a warm up period has been allowed for, the sensor should be checked to verify sensitivity to gas.
Material Requirements
* Digital volt meter
* Jewelers type screwdriver
* Detcon PN 943-000006-132 Threaded Calibration Adapter
* Span Gas 50% LEL methane in air at a controlled flow rate of 200 ml/min.
a) Declassify the area around the sensor.
b) Remove the junction box cover.
c) Measure the voltage between the bridge test points: The bridge voltage is factory set at 2.7V. Use the
“Temp” potentiometer to make adjustments if necessary. (Note: If the sensor head has been remotely
installed away from the transmitter, the bridge voltage must be measured at the sensor head instead of
the bridge test points. The voltage is measured between the blue and white wires and should be adjusted to 2.7vdc.)
d) Measure the voltage between the signal test points: zero gas conditions should provide a reading of
between 39 and 40 mV DC. If necessary, adjust the zero potentiometer to achieve this reading.
e) If applicable, remove the rain shield or splash guard from the sensor housing.
f) Attach the calibration adapter to the threaded sensor housing. Apply the test gas at a controlled flow rate of
200 ml/m. Observe that the signal voltage increases to a level of 80 mV DC or higher.
g) Remove the test gas and observe that the signal decreases to between 39 and 40 mV DC.
Initial operational tests are complete. Detcon Model series FP-424C sensors are pre-calibrated prior to ship-
Detcon Model FP-424C Combustible Gas Sensor PG.11
ment and will, in most cases, not require significant adjustment on start up. However, Detcon recommends
hat a complete calibration test and adjustment be performed within 24 hours of installation. Refer to cali-
t
bration instructions in later text.
7.0 CALIBRATION PROCEDURE
7.1 Material Requirements
* Digital volt meter
* Jewelers type screwdriver
* Detcon PN 943-000006-132 Threaded Calibration Adapter
* Span Gas 50% LEL methane in air at a controlled flow rate between 200 ml/min.
7.2 Calibration
1) Declassify the area around the sensor.
2) Remove the junction box cover.
3) Measure the voltage between the bridge test points: The bridge voltage is factory set at 2.7V. Use the
temp potentiometer to make adjustments if necessary.
4) Measure the voltage between the signal test points: zero gas conditions should provide a reading of
between 39 and 40 mV DC. If necessary, adjust the zero potentiometer to achieve this reading.
5) If applicable, remove the rain shield or splash guard from the sensor housing.
6) Attach the calibration adapter to the threaded sensor housing. Apply the test gas at a controlled flow rate of
200 ml/m. Allow 1-2 minutes for signal stability.
7) Measure the voltage between the signal test points. Use the coarse potentiometer to adjust the signal to
a reading of 120 mV DC. Use the fine potentiometer to make finer adjustments as needed.
8) Remove the test gas and observe that the signal decreases to between 39 and 40 mV DC.
Note: Because there is interaction between the span and zero functions, it may be necessary to repeat steps 4 through 8.
Calibration is complete. Replace the rain shield or splash guard and junction box cover.
7.3 Calibration Notes
Detcon Model FP-424C series sensors provide a signal output of 4-20 mA DC which corresponds to 0-100%
LEL. This signal is reflected by a 40-200 mV DC voltage across the signal test points. Therefore the signal
output will move by .16 mA (or 1.6 mV across the signal test points) for each 1% of movement.
If calibration is being done with a gas concentration other than 50% LEL, you can determine the proper signal voltage by dividing 160 mV by 100 and then multiplying that figure by the concentration of gas. For
example, if you are calibrating a sensor with a gas standard that contains 10% LEL, you would divide 160
(mV) by 100 (%) and then multiply that figure by 10 (%). Then add the base line of 40 (mV) to arrive at the
proper signal voltage of 56 mV. Refer to the chart below for some sample signal outputs with different gas
concentrations applied.
% LEL Signal Reading
0 40 mV
10 56 mV
25 80 mV
50 120 mV
75 160 mV
100 200 mV
7.4 Calibration Frequency
In most applications, monthly to quarterly calibration intervals will assure reliable detection. However,
industrial environments differ. Upon initial installation and commissioning, close frequency tests should
be performed, weekly to monthly. Records should be kept. Less frequent test schedules should be implemented based on analysis of tests prior to adjustment.
Detcon Model FP-424C Combustible Gas Sensor PG.12
8.0 FAULT SUPERVISION
Model FP-424C sensors incorporate fault circuitry which monitors both the detector loop and the bridge
voltage of the catalytic bead sensor element. Should one or both of the catalytic bead circuits become electrically “open” a Detector Fault condition will occur which will result in the illumination of the “DET FLT”
ED located on the transmitter face plate. Should the bridge voltage drop below 1.8 V, a Bridge Fault con-
L
dition will occur which will result in the illumination of the “BRDG FLT” LED located on the transmitter
face plate. Either fault condition will cause the 4-20 mA signal to drop to 0 mA. When used with Detcon
Model 10 or Model 12 controls, this drop in the mA signal will result in a fault condition on the affected
control module creating a dual redundant fault function.
9.0 TR
Detector Fault
1. Open Sensor – broken wire or contact in sensor.
2. Remove replaceable sensor element and check adjacent pin pairs with ohm-meter. Normal reading is 1-
3. Replace sensor if verified as Open Sensor.
Bridge Fault
1. Shorted detector bead, shorted transmitter, or faulty transmitter.
2. Make sure that there is no presence of condensation or accumulated water in the sensor housing or cond-
3. Swap in new transmitter and/or new sensor.
Poor Sensor Performance (Slow Response, Drifting Sensor)
1. Check that correct Heater Voltage is applied to your sensor.
Note: Detcon has two version sensors: C-Style and the J-Style. Each uses a different heater voltage setting.
The C-Style sensor measures 0.9'' across the exposed stainless steel sinter face and has a serial number format C??-###. The C-Style sensor requires 2.7 VDC
The J-Style sensor measures 0.4”across the exposed stainless steel sinter face and has a serial number format J??-###. The J- Style sensor requires 2.2 VDC.
OUBLESHOOTING
4 ohms and failed reading is an open circuit.
ulet. This could cause possible shorting.
GU
IDE
2. If heater voltage is incorrect then adjust it accordingly for the sensor type.
Excessive Span Drift or Slow Response
1. Check Heater Voltage Setting (should be 2.7V C-Style and 2.2V J-Style) and check heater voltage at the
sensor if remote mounted.
2. Verify correct cal gas flow rate and proper use of the cal gas adapter.
3. Check validity of cal gas via the expiration date and use pull tube if necessary.
4. Check for obstructions through stainless steel sinter element (including being wet).
5. Replace plug-in sensor if necessary.
6. Check area for presence of sensor poisoning gases such as silicon grease vapors, HMDS, high H2S, chlo-
rine or chlorinated compounds if sensor failures persist.
Drifting Zero
1. May be correct reading if there are real gas leaks or the sensor was zero calibrated when actual gas was
around and subsequently cleared.
2. Check Heater voltage is set correctly for sensor type (check voltage at the sensor if remote mounted).
3. Replace sensor if sensor has experienced large span losses that exaggerate zero drift.
4. If sensor drift is gradual and continuously positive (with a stable span) then contact Detcon for sensor
replacement.
Detcon Model FP-424C Combustible Gas Sensor PG.13
Unstable Output/ Sudden Spiking/Nuisance Alarms
Rain Shield
Cal ibra tion Adap ter
FP-424C Transmitter Assembly
Sensor Terminal Board
Enclosure Cover
Enclosure
Sensor: field replaceable plug-in detector
LEL Main Sensor Housing Assembly
Condensation
Prevention Packet
(replace annually)
. Check condulet for accumulated water.
1
2. Check transmitter and Terminal PCB for abnormal corrosion.
3. Determine if problem correlates with condensation cycles.
4. Add/change Detcon condensation prevention packet
PN 960-202200-000 (replace annually).
5. Check for unstable power supply.
6. Check for inadequate grounding.
7. If correlates with radio communications then use Detcon RFI filter accessory.
8. Contact Detcon for assistance in optimizing shielding, grounding, and RFI protection.
Transmitter not Responding
1. Verify condulet has no accumulated water or abnormal corrosion.
2. Verify required DC power is applied to correct terminals.
3. Swap with a known-good transmitter to determine if transmitter is faulty.
Bad 4-20 mA output
1. Check that wiring is connected to correct terminal outputs.
2. Swap with a known-good transmitter to determine if transmitter is faulty.
10.0 SPARE PARTS LIST
613-010000-000 Sensor rain shield
613-120000-000 Sensor splash guard
943-000006-132 Threaded Calibration Adapter
612-820000-000 LEL sensor housing assembly (plug-in detector, PN 370-201600-000, not included)
370-201600-000 Sensor: field replaceable plug in detector
500-005065-007 Terminal Connector Board
897-850800-000 NEMA 7 enclosure less cover - 3 port
897-850400-000 NEMA 7 enclosure cover
960-202200-000 Condensation prevention packet (replace annually)
924-525400-100 FP424C Plug-in control circuit
Detcon Model FP-424C Combustible Gas Sensor PG.14
11.0 WARRANTY
Detcon, Inc., as manufacturer, warrants each new LEL plug-in detector (PN 370-201600-000), for a two year
period under the conditions described as follows: The warranty period begins on the date of shipment to
the original purchaser and ends two years thereafter. The sensor element is warranted to be free from
efects in material and workmanship. Should any sensor fail to perform in accordance with published
d
specifications within the warranty period, return the defective part to Detcon, Inc., 3200 Research Forest
Dr., Suite A-1, The Woodlands, Texas 77381, for necessary repairs or replacement.
12.0 SERVICE POLICY
Detcon, Inc., as manufacturer, warrants under intended normal use each new sensor signal transmitter to
be free from defects in material and workmanship for a period of two years from the date of shipment to
the original purchaser. Detcon, Inc., further provides for a five year fixed fee service policy wherein any
failed transmitter shall be repaired or replaced as is deemed necessary by Detcon, Inc., for a fixed fee of
$35.00. The fixed fee service policy shall effect any factory repair for the period following the two year warranty and shall end five years after expiration of the warranty. All warranties and service policies are FOB
the Detcon facility located in The Woodlands, Texas.
Shipping Address: 3200 Research Forest Dr., Suite A-1, The Woodlands, Texas 77381
Mailing Address: P.O. Box 8067, The Woodlands, Texas 77387-8067
phone 888-367-4286, 281-367-4100 • fax 281-292-2860 • www.detcon.com • sales@detcon.com
Detcon Model FP-424C Combustible Gas Sensor PG.15
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