Det-Tronics R8471A User manual

Instructions 95-8398-02
Combustible Gas Controller
R8471A
Detector Electronics Corporation
6901 West 110th Street •Minneapolis, Minnesota 55438 USA
Tel: [phone] or 800.765.3473 •Fax: [phone]

Section I - General Information
DESCRIPTION..........................................................1
FEATURES................................................................1
SPECIFICATIONS.....................................................1
SYSTEM OPERATION..............................................3
Sensor.................................................................3
Transmitter..........................................................3
Controller.............................................................3
Faceplate Description...................................3
Setpoints.......................................................4
Outputs.........................................................4
Automatic Diagnostics and Fault
Identification...........................................4
Operating Modes..........................................5
Section II - System Installation
INSTALLATION.........................................................7
Sensor Location ..................................................7
General Wiring Requirements.............................8
Sensor Separation...............................................9
Kit Description...............................................9
Sensor Installation......................................10
Wiring Requirements..................................10
Sensor Voltage Adjustment (K Series).......10
Sensor/Transmitter Wiring (without Sensor ...
Separation).................................................11
Controller Wiring................................................12
Field Wiring Connector...............................12
Controller Programming....................................15
Normally Open/Closed Relays....................15
Latching/Non-Latching Relays....................16
Normally Energized/De-Energized Relays .16
4 to 20 ma Output.......................................16
INSTALLATION CHECKLIST..................................16
Section III - System Startup
STARTUP PROCEDURE........................................16
SETPOINT ADJUSTMENT......................................17
Setpoint Display Mode ......................................17
Setpoint Adjustment Procedure.........................17
CALIBRATION.........................................................18
Conversion (K) Factor.......................................18
Calibration Procedure........................................19
Setting Controller Default Values................20
Transmitter Calibration Procedure
(K Series) .............................................20
Alternate Transmitter Calibration Procedure
(K Series) .............................................20
Controller Calibration Procedure ................22
Current Output Calibration ................................22
Section IV - System Maintenance
ROUTINE MAINTENANCE .....................................23
Manual Check of Output Devices......................23
Checkout in Normal Mode.................................23
Sensor Replacement.........................................23
Controller Calibration..................................24
Transmitter Calibration ...............................24
TROUBLESHOOTING.............................................24
LOSS OF SENSOR SENSITIVITY..........................24
REPLACEMENT PARTS.........................................26
DEVICE REPAIR AND RETURN ............................26
ORDERING INFORMATION...................................28
List of Illustrations
Figure 1 Controller Dimensions in Inches
(Centimeters)..........................................2
Figure 2 Controller Front Panel............................3
Figure 3 R8471 Controller Flow Chart..................6
Figure 4 Typical Installation Using Sensor Separa-
tion Kit with K Series Transmitter...........9
Figure 5 Sensor Separation with K Series
Transmitter...........................................11
Figure 6 Transmitter Wiring................................12
Figure 7 Dimensions of the Mounting Rack........13
Figure 8 Clip Positioning for Mounting Racks.....13
Figure 9 Terminal Configuration for R8471
Combustible Gas Controller.................14
Figure 10 A Typical System with Relay Outputs and
Non-Isolated Current Output................14
Figure 11 A Typical System with Relay Outputs and
Isolated Current Output........................14
Figure 12 Open Collector Output with Inductive Load
and Transient Suppression Device ......15
Figure 13 Programming Jumper Plugs and
Switches...............................................15
Figure 14 Calibration Sequence for K Series
Transmitter...........................................21
List of Tables
Table 1 Selectable Relay Options.......................2
Table 2 System Status Codes.............................5
Table 3 Maximum Wiring Distances - Controller
to K Series Transmitter...........................9
Table 4 Maximum Separation Distances - Sensor
to K Series Transmitter.........................10
Table 5 Troubleshooting Guide.........................25
Table of Contents
ii

Section I
General Information
DESCRIPTION
The R8471A Combustible Gas Controller monitors a 4
to 20 milliampere (ma) dc signal generated by a Det-
Tronics combustible gas sensor/transmitter assembly.
The single channel system operates in the range of 0
to 100% LFL (lower flammable limit). Controller
response includes actuation of solid state or optional
relay outputs for direct control of field response
devices, a full array of faceplate indicators, as well as
an optional 4 to 20 ma output for transmitting system
information to other monitoring devices.
FEATURES
•Controller accepts a 4 to 20 ma input, ensuring
compatibility with a variety of transmitters.
•Digital display, bar graph display, and high intensity
LEDs indicate important system status information.
•AutoCal feature ensures easy and accurate calibra-
tion.
•Microprocessor based controller is easily field pro-
grammable to meet the needs of a specific applica-
tion.
•Base model is furnished with solid state alarm and
fault outputs.
•Premium model is furnished with relay outputs and a
4 to 20 ma dc output.
•Current output is selectable for isolated/non-isolated
operation.
•Rack compatible with Det-Tronics R7400 series
flame controllers.
•Variety of racks available in 4U or 3U height config-
uration.
SPECIFICATIONS
CONTROLLER
OPERATING VOLTAGE—
24 vdc. Can operate in the range of 18 to 32 vdc.
MAXIMUM RIPPLE—
Ripple should not exceed 5 volts peak-to-peak. The
sum of dc plus ripple must be ≥18 vdc and ≤32 vdc.
POWER CONSUMPTION (controller only)—
Base model: 0.7 watt nominal, 1.3 watts maximum
(25 ma nominal, 50 ma maximum at 24 vdc.)
Premium model: 1.2 watts nominal, 3.5 watts maxi-
mum (50 ma nominal, 145 ma maximum at 24 vdc.)
TEMPERATURE RANGE—
Operating: +32°F to +140°F (0°C to +60°C)
Storage: –49°F to +185°F (–45°C to +85°C).
HUMIDITY RANGE—
5 to 99% RH, non-condensing.
OPERATING RANGE—0 to 100% LFL.
ACCURACY—
±3% of full scale over specified temperature range.
SOLID STATE OUTPUTS (Base model only)—
The outputs are open collector transistors with a 100K
resistor from the collector to emitter with the emitter
grounded, rated 100 ma at 32 volts dc maximum.
RELAY CONTACTS (Premium model only)—
Selectable normally open/normally closed contacts
rated 5 amperes at 30 vdc/250 vac. See Table 1 for
selectable relay options.
CURRENT OUTPUT (Premium model only)—
4 to 20 ma dc current, with a maximum loop resis-
tance of 600 ohms at 20 to 32 vdc.
INSTRUCTIONS
Combustible Gas Controller
R8471A
©Detector Electronics Corporation 1995 2/95 95-8398-02
DET-TRONICS®

DIMENSIONS—
See Figure 1.
SHIPPING WEIGHT (approximate)—
2.0 pounds (0.9 kilogram).
K SERIES TRANSMITTER
INPUT VOLTAGE—
24 vdc (10 to 28 vdc range).
POWER CONSUMPTION—
1.5 watts with sensor.
OUTPUT CURRENT—
Linear 4 to 20 ma.
ZERO SHIFT WITH TEMPERATURE—
0.02% LFL/°C at maximum gain.
GAIN SHIFT WITH TEMPERATURE—
0.01% LFL/°C at maximum gain.
TEMPERATURE RANGE—
Operating: 0°F to +167°F (–40°C to +75°C).
Storage: –49°F to +185°F (–45°C to +85°C).
SENSOR
RESPONSE TIME (with full scale gas applied)—
10 seconds to reach 50 percent of value of applied
gas, and 30 seconds to reach 90 percent of value of
applied gas.
ACCURACY—
±3 percent full scale up to 2.5 percent methane gas
by volume in air (50% LFL), ±5 percent full scale up
to 5 percent methane gas by volume in air (100%
LFL).
REPEATABILITY—
±5 percent, full scale.
ZERO DRIFT—
Less than 1% LFL per month.
OXYGEN EFFECTS—
The sensor will operate normally with the oxygen level
in the atmosphere at or above 10 percent concentra-
tion. Under oxygen enriched conditions the sensor
will respond normally, but the user should beware of
an increase in the explosive hazard. Contact the fac-
tory for information regarding use of the sensor in oxy-
gen deficient atmospheres.
HUMIDITY RANGE—
0 to 99% RH, non-condensing.
HUMIDITY EFFECT—
Less than ±5 percent full scale deviation at 10% to
90% RH.
SYSTEM APPROVAL—
The R8471A Combustible Gas Controller, base and
premium model in 3U and 4U height, has been tested
and approved by FMRC. It can be used with any
FMRC approved gas sensing device capable of gen-
erating a 4 to 20 ma input.
FMRC approval of the R8471A Combustible Gas
Controller, however, does not include or imply
approval of input devices such as sensors or trans-
mitters, or devices connected to the controller out-
puts. To maintain FMRC system approval, all equip-
ment connected to the controller must be FMRC
approved. Note that while the Det-Tronics com-
bustible gas sensor and K Series transmitter are fully
compatible with the R8471A Controller, they have not
been FMRC tested and approved for use with the
R8471A Controller.
2
Figure 1—Controller Dimensions in Inches (Centimeters)
Table 1—Selectable Relay Options
Relay Selectable Selectable Selectable
Normally Normally Latch/
Open/Closed Energized/ Non-Latch
De-Energized
Low Y Y Y
High Y Y N1
Auxiliary Y Y Y
Fault Y N2N3
Y = Yes N = No 1Latching only
2Normally energized 3No latching option
➛
➛
9.3 (23.6)
1.0
(2.5)
7.0*
(17.8)
➛
➛
➛
➛
A1526 *4U DIMENSIONS SHOWN, 3U HEIGHT IS 5.2 (13.3)

SYSTEM OPERATION
SENSOR
Det-Tronics combustible gas sensors use a catalytic
type sensing element and operate in the range of 0 to
100% LFL. Sensors are available in aluminum or
stainless steel housings, with a choice of three sens-
ing elements - standard, poison resistant, and high
temperature. With proper calibration, the sensor can
be used to detect a wide variety of combustible
gases. Contact Detector Electronics for assistance in
adapting the sensor to a specific application.
TRANSMITTER
The transmitter functions as the interface between the
sensor and the controller. It regulates operating
power to the sensor and generates a linear 4 to 20 ma
output signal proportional to 0 to 100% LFL com-
bustible gas concentration.
A transmitter output signal of less than 4 ma is dis-
played as a negative reading by the controller.
The sensor is normally threaded directly to the trans-
mitter enclosure. However, the sensor and transmitter
can be mounted separately using a Sensor
Separation Kit available from Detector Electronics.
The sensor, transmitter and separation kit are
designed for use in hazardous areas, and when prop-
erly installed will provide an explosion-proof installa-
tion.
Detector Electronics offers a variety of transmitter
models that operate in the 0 to 100% LFL range and
are compatible with the R8471 Controller. Refer to
the “Ordering Information” section for more informa-
tion.
CONTROLLER
Faceplate Description
The faceplate of the controller provides LEDs for iden-
tifying status conditions, a digital display and bar
graph display for indicating the sensor input, and
pushbuttons for programming, calibrating and reset-
ting the system. See Figure 2 for the location of indi-
cators and pushbuttons.
1. Digital Display—The digital display continuously
provides a % LFL reading of the sensor input in
both the Normal and Calibrate modes. In the
event of a fault, it identifies the nature of the fault
using an alpha-numeric code. In other operating
modes it shows the alarm setpoints and pro-
grammed calibration gas concentration. A nega-
tive zero drift condition is indicated by a minus (–)
sign in the left hand digit. If an over-range condi-
tion occurs, the display flashes and the highest
reading latches on. Since this display is always
on, it also functions as a power indicator.
2. Bar Graph Display—The 20 segment bar graph
display provides a reading of sensor input in 5%
LFL increments.
3. High Alarm LED—Flashes in response to a sensor
signal that exceeds the high setpoint.
4. Auxiliary Alarm LED—Flashes in response to a
sensor signal that exceeds the auxiliary setpoint.
5. Low Alarm LED—Flashes in response to a sensor
signal that exceeds the low setpoint.
NOTE
The alarm LEDs flash when the setpoint is
exceeded and are on steady (until reset) when
the gas level drops below the setpoint, whether
the corresponding alarm output is latching or
non-latching.
3 95-8398
Figure 2—Controller Front Panel

6. Cal LED—Illuminated while the controller is in the
calibrate mode.
NOTE
In the Setpoint Display or Setpoint Adjust mode,
a flashing alarm LED identifies the particular set-
point currently being indicated on the digital dis-
play. A flashing Cal LED indicates that the pro-
grammed calibration gas concentration in % LFL
is currently being shown on the digital display.
7. Fault LED—Flashes upon detection of a system
fault and is on steady during the power-up time
delay.
8. Reset Pushbutton—Used for various system pro-
gramming and calibration functions as well as for
resetting the controller.
9. Set Pushbutton—Used for various system pro-
gramming and calibration functions.
Setpoints
The R8471 Controller has independent Low, High,
and Auxiliary alarm setpoints, with corresponding out-
puts.
The programmed calibration gas concentration in %
LFL is also displayed and adjusted with the alarm set-
points. This value must be equal to the % LFL con-
centration of the calibration mixture that is used for
the span adjustment.
The adjustment range is:
Low alarm 5 to 50% LFL
High alarm 10 to 60% LFL
Auxiliary alarm 5 to 90% LFL
Calibration gas 30 to 99% LFL.
The alarm setpoints and calibration gas concentration
can be checked by pressing the Reset pushbutton
located on the front panel of the controller. See
“Setpoint Adjustment” and “Calibration” sections.
Outputs
The R8471 Controller is available in a Base version
and a Premium version. The differences between the
two models are the output configuration and program-
ming options.
Base Model—The base controller is furnished with
open collector transistor outputs (rated 100 ma at 32
volts dc) for the Low alarm, High alarm, Auxiliary
alarm, and Fault circuits. The normally de-energized
alarm outputs are energized when their correspond-
ing setpoints are exceeded. The fault output is nor-
mally energized and becomes de-energized upon
detection of a system fault.
Premium Model—The premium model is furnished
with a set of four relays in place of the four solid state
outputs. The relays have SPST contacts rated 5
amperes at 30 vdc or 250 vac.
This model also includes a selectable isolated/non-
isolated 4 to 20 ma dc current output for transmitting
system information to other monitoring devices. The
linear 4 to 20 ma output corresponds to levels from 0
to 100% LFL. If a system fault is detected, the output
drops to less than 1.0 ma. The current output can be
calibrated in the field to ensure maximum accuracy.
(Refer to the “Calibration” section for details.)
Programming Options (Premium model only)—Each of
the four relays is field selectable for either normally
open or normally closed contacts using jumper plugs
located on the printed circuit board inside the con-
troller. (See Table 1.)
The alarm relays are also switch programmable for
either normally energized or normally de-energized
operation. The fault relay is normally energized.
The low and auxiliary alarm relays are programmable
for either latching or non-latching operation. The high
alarm relay is always latching and the Fault relay is
non-latching. Latching relays are reset using either
the Reset pushbutton on the front panel of the con-
troller or an external reset switch.
The 4 to 20 ma circuit is selectable for isolated or
non-isolated operation.
Automatic Diagnostics and Fault Identification
The microprocessor based controller features self-
testing circuitry that continuously checks for faulty
sensor or open sensor wiring, low or high input volt-
age, and other problems that could prevent proper
system response. When power is applied, the micro-
processor automatically tests memory. In the Normal
operating mode, it continuously monitors the input
signal from the transmitter to ensure proper function-
ing. In addition, a “watchdog” timer is maintained to
ensure that the program is running correctly. If a fault
should occur:
— The Fault LED flashes.
— The digital display identifies the nature of the fault
using an alpha-numeric code. Refer to Table 2.
— The normally energized Fault output is de-ener-
gized.
— The dc current output drops to less than 1 ma.
4

NOTE
The fault code will be shown for about 2 seconds
out of every 5 seconds. The gas concentration
at the sensor will be displayed during the remain-
ing time. If more than one fault should occur, the
highest priority fault will be displayed. (Table 2
lists the faults in order of priority.)
An alarm condition will normally over-ride a fault con-
dition unless the fault condition occurred first (except
F10, F2X). However, faults that affect the actual func-
tion of the controller (F50, F60, F70, F9X) can impair
the ability of the controller to maintain an alarm out-
put.
All faults automatically reset except the F9X, F20, and
F10 faults. After the fault condition has been correct-
ed, the fault output automatically switches to the nor-
mal (energized) state, the dc current output returns to
normal, and the Fault LED turns off. Clearing F9X
faults requires removing operating power from the
controller for approximately one second.
CAUTION
The fault detection circuitry does not monitor the
operation of external response equipment or the
external wiring to these devices. It is important
that these devices be checked periodically to
ensure that they are operational.
Operating Modes
NOTE
The following section is intended to acquaint the
operator with the basic operation of the con-
troller. For complete step-by-step programming
and calibration procedures, refer to the corre-
sponding sections in this manual.
The controller can operate in any of the following
modes. Operating modes other than Normal are
selected by pressing the appropriate pushbutton(s)
located on the controller front panel. See Figure 3.
NORMAL
In the Normal operating mode with no alarm condi-
tion:
— Digital display is on and indicates the sensor input
in % LFL.
— Bar graph display reads the same as the digital
display.
— All LEDs are off.
— Alarm outputs are in their normal state (energized
or de-energized as programmed).
— DC current output signal level corresponds to sen-
sor input.
— Fault output is energized.
In the Normal operating mode with a low and/or auxil-
iary alarm condition occurring:
— Digital display and bar graph display indicate the
sensor input in % LFL.
— Low and/or Auxiliary LED flashes.
5 95-8398
Table 2—System Status Codes
Status Condition
F9X Initialization failure. (Subcodes are as fol-
lows.)
F91 EPROM sumcheck failure.
F92 Sensor failure during startup - current too
high or too low.
F93 Watchdog timer failure.
F94 RAM failure.
F95 Internal 5 volt power supply failure during
startup.
F96 External 24 volt power supply failure dur-
ing startup.
F97 Controller type invalid. Error in data from
RAM.
F98 Watchdog timer reset the controller.
F70 External reset button has been activated
for 15 seconds or longer. Self clearing
when button is released.
F60 External 24 vdc power input is not in the
18 to 32 vdc range.
F50 Internal 5 volt power supply is not in the
4.75 to 5.25 volt range.
F40 Sensor fault (after startup). Input is above
35 ma or below 2 ma.
F30 Negative zero drift. Sensor input is –9%
full scale or lower.
F2X Calibration error. (Subcodes are as fol-
lows.)
F20 General calibration fault, or calibration
aborted due to a higher priority fault.
F21 Time ran out while waiting for calibration
gas to be applied to the sensor.
F22 Sensor input is too low. The sensor cannot
generate enough offset to get an accurate
calibration. Replace sensor.
F23 Sensor is too sensitive for the controller to
read 100% full scale. Replace sensor.
F24 Zero gas level too high, or sensor zero
input over limit.
F10 Sensor reaching end of life. Consider
replacing the sensor within the next two
calibration periods.

— Low and/or Auxiliary alarm output changes state.
— Dc current output signal level corresponds to sen-
sor input.
— Fault output energized and LED off.
When the signal decreases below the low or auxiliary
setpoint:
— Digital display, bar graph display, and 4 to 20 ma
output continue to track the sensor input.
— With latching operation programmed: No change
to alarm outputs.
— With non-latching operation programmed: Alarm
outputs return to their normal state.
— Low and Auxiliary LEDs are on steady until reset.
In the Normal operating mode and a high alarm con-
dition occurring:
— Same as low or auxiliary alarm, but High LED is on
and high alarm output is actuated.
When the signal decreases below the high alarm set-
point:
— The high alarm is always latching and unaffected
by the latching/non-latching programming for the
low and auxiliary alarms. High LED is on steady
until reset.
In the event of a system fault:
— The normally energized Fault output is de-ener-
gized and the Fault LED is illuminated.
RESET
The Reset mode is the first mode that is entered by
pressing the Reset button located on the front panel
of the controller. (See Figure 3.) When the Reset but-
ton is momentarily depressed,all LEDs turn off and
all outputs return to their normal condition if no alarms
or faults are occurring (basic reset). When the Reset
button is held for 0.5 second,the LEDs turn off and
the outputs return to their normal condition even if an
alarm or fault condition still exists (forced reset).
Remote reset capability is also provided. (Remote
reset performs a forced reset.)
NOTE
The remote reset performs a reset function
only. It cannot be used for entering other
controller operating modes.
SETPOINT DISPLAY MODE
If the Reset button is held for approximately one sec-
ond, the digital display sequentially shows the pro-
grammed alarm setpoints and calibration gas con-
6
Figure 3—R8471 Controller Flow Chart
POWER-UP
TIME
DELAY
NORMAL RESET
< 0.5 SECOND 0.5 SECOND 1.0 SECOND
HOLD RESET
7 SECONDS
SET
1.0 SECOND
NO
YES
BASIC
RESET FORCED RESET
RELEASE
RESET
RELEASE
RESET
RELEASE
RESET
SETPOINT
DISPLAY
HOLD
RESET
HOLD
RESET
HOLD
RESET
SENSOR
REPLACE
SETPOINT
ADJUST
CURRENT
CALIBRATE
RESET
PUSHED WITH
SET?
CALIBRATE
9.0 SECONDS
SET*
RESET
*MUST BE PRESSED BEFORE THE ZERO
CALCULATIONS ARE COMPLETED.
D1385

centration. Each value is displayed for approximately
2 seconds. After completing the sequence, the con-
troller automatically returns to the Normal operating
mode if the Reset button is no longer being
depressed.
This mode is used only for displaying the setpoints.
Use the “Setpoint Adjust” mode for changing setpoint
and calibration gas values.
CALIBRATE
The R8471 Controller uses a fully automatic calibra-
tion procedure that requires no adjustments to be
made by the operator. The Calibrate mode is entered
by pressing and holding the Reset button until com-
pletion of the “Setpoint Display” sequence described
above (approximately 9 seconds). The controller per-
forms the Zero adjustments, then signals the operator
when to apply and also when to remove the calibra-
tion gas. Upon completion of a successful calibra-
tion, the controller automatically returns to the Normal
operating mode.
If the operator fails to complete the calibration proce-
dure, if an error in calibrating occurs, or if a success-
ful calibration cannot be completed, the microproces-
sor will automatically return to the Normal mode (after
10 minutes) and continue to use the previous calibra-
tion data. A fault indication (“F2X” status) will be dis-
played until a reset occurs. If the microprocessor
determines that the sensing element is approaching
the end of its useful life, “F10” will be indicated on the
digital display. Refer the “Calibration” section for
complete information regarding calibration.
While in the Calibrate mode, all controller outputs are
inhibited, the CAL LED is illuminated, and the dc cur-
rent output goes to a preset level (adjustable from 0
to 20 ma).
SENSOR REPLACEMENT
This mode inhibits all controller outputs to allow sen-
sor replacement without removing power from the
controller. In addition, this mode automatically sets
the factory default values for sensor calibration.
Other programmed setpoint values are not affected.
CAUTION
Upon entering the Sensor Replacement mode,
all previously entered sensor calibration informa-
tion is lost. Sensor calibration must be per-
formed, even if the sensor was not replaced.
To enter the Sensor Replacement mode, first enter the
Calibrate mode as described above, then press the
Set button. To exit this mode, press the Reset button.
SETPOINT ADJUST
The Setpoint Adjust mode is entered by depressing
the Set button for approximately one second. In this
mode the alarm setpoints and calibration gas level
are sequentially displayed on the digital display for
approximately five seconds and the corresponding
LED flashes. To change the setpoint, depress the
Reset button to increase the displayed value or the
Set button to decrease the value. If no changes are
made for 5 seconds, the microprocessor automatical-
ly advances to the next setpoint. At the end of the
sequence, the microprocessor automatically returns
to the Normal operating mode.
DC CURRENT OUTPUT CALIBRATION
This mode is used to calibrate the 4 to 20 ma dc out-
put. To enter this mode, hold the Set button, then
press Reset. First the 0% LFL value (4 ma) is gener-
ated for approximately 7 seconds while the Low LED
flashes. Then the 100% LFL value (20 ma) is generat-
ed while the High LED flashes. Finally the current out-
put during calibration is generated while the CAL LED
flashes. The microprocessor automatically returns to
the normal operating mode at the end of the
sequence. Adjustments to the current output level
are made by pressing the Reset (increase) or Set
(decrease) button. This procedure requires a dc cur-
rent meter to monitor the actual controller dc mil-
liampere output.
Section II
System Installation
INSTALLATION
NOTE
The sensor is not included in the FMRC
approval.
NOTE
Refer to the sensor manual for complete infor-
mation regarding sensor installation.
SENSOR LOCATION
It is essential that the sensor be properly located to
enable it to provide maximum protection. The formula
for determining the most effective number and place-
ment of sensors varies depending on the conditions
at the job site. The individual performing the installa-
tion must rely on experience and common sense to
determine the quantity of sensors and the best sensor
locations to adequately protect the area.
7 95-8398

For additional information on determining quantity and
placement for sensors in a specific application, refer
to Instrument Society of America (ISA) Transaction
Volume 20, Number 2, titled “The Use of Combustible
Detectors in Protecting Facilities from Flammable
Hazards”.
The following factors should be considered for every
installation:
1. What kind of gas is to be detected? If it is lighter
than air (acetylene, hydrogen, methane, etc.),
place the sensor above the potential gas leak.
Place the sensor close to the floor for gases that
are heavier than air (benzene, butane, butylene,
propane, hexane, pentane, etc.) or for vapors
resulting from flammable liquid spills. However,
note that air currents can cause a gas that is
heavier than air to rise. In addition, if the gas is
hotter than ambient air, it could also rise.
2. How rapidly will the gas diffuse into the air?
Select a location for the sensor as close as practi-
cal to an anticipated source.
3. Ventilation characteristics of the immediate area
must also be considered. Movement of air can
cause gas to accumulate more heavily in one
area than another. The sensor should be placed
in the area where the most concentrated accumu-
lation of gas is anticipated. Also consider the fact
that many ventilation systems do not operate con-
tinuously.
4. The sensor should be pointed down to prevent
the buildup of moisture or contaminants on the fil-
ter and to ensure proper operation.
5. The sensor must be accessible for testing and
calibration. The use of the Sensor Separation Kit
will be required in some installations.
6. The sensor should be located in an area where it
is safe from potential sources of contamination
that can poison the sensing element.
7. Exposure to excessive heat or vibration can result
in premature failure of any electronic device and
should be avoided if possible. Shielding the
device from intense sunlight will reduce solar
heating and can increase the life of the unit.
Remember, the finest gas detector is of little value if
the gas cannot readily come into contact with it.
GENERAL WIRING REQUlREMENTS
NOTE
The wiring procedures in this manual are intend-
ed to ensure proper functioning of the device
under normal conditions. However, because of
the many variations in wiring codes and regula-
tions, total compliance to these ordinances can-
not be guaranteed. Be certain that all wiring
complies with applicable regulations that relate to
the installation of electrical equipment in a haz-
ardous area. If in doubt, consult a qualified offi-
cial before wiring the system.
In applications where the wiring cable is installed in
conduit, the conduit must not be used for wiring to
other electrical equipment.
The use of shielded cable is recommended for con-
necting the transmitter to the controller. If a sensor
separation kit is used, shielded cable must be used
between the sensor and the transmitter.
Since moisture can be detrimental to electronic
devices, it is important that moisture not be allowed to
come in contact with the electrical connections of the
system. Moisture in the air can become trapped with-
in sections of conduit. Therefore, the use of conduit
seals is required to prevent damage to electrical con-
nections caused by condensation within the conduit.
These seals must be watertight and explosion-proof
and are to be installed even if they are not required
by local wiring codes. A seal must be located as
close to the device as possible. In no case should this
seal be located more than 18 inches (46 cm) from the
device. When an explosion-proof installation is
required, an additional seal may be needed at any
point where the conduit enters a non-hazardous area.
Always observe the requirements of local codes.
When pouring a seal, the use of a fiberdam is
required to assure proper formation of the seal. The
seals should never be poured in temperatures that
are below freezing, since the water in the sealing
compound will freeze and the compound will not dry
properly. Contamination problems can then result
when temperatures rise above the freezing point and
the compound thaws.
The shielding of the cable should be stripped back to
permit the seal to form around the individual leads,
rather than around the outside of the shield. This will
prevent any siphoning action that can occur through
the inside of the shield.
8