SAFETY SYSTEMS TECHNOLOGY NOVA-Sensor GIR901 Guide

Model GIR901
Infrared Combustible Gas
NOVA-Sensor
DESIGN MANUAL
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SYSTEMS TECHNOLOGY in writing. Such
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The information in this document is applicable to
sensors built on or after October, 2001

Quick Finder - Model GIR901 Infrared Combustible
Gas NOVA-Sensor
QUICK START . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .901-1
Apply Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .901-1
Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .901-1
Alarm Setpoints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .901-1
DIP Switch: Latch/No Latch Setting for LOW Alarm Output . . . . . . . . . . . . . . . . .901-1
DESCRIPTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .901-2
Principle of Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .901-2
Detectable Gases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .901-3
TECHNICAL SPECIFICATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .901-4
INSTALLATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .901-4
Installation Sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .901-5
Mounting the enclosure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .901-5
Wiring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .901-6
Remote Sensor Version . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .901-7
DIP Switch settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .901-8
OPERATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .901-9
Power-Up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .901-9
Changing the Setpoints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .901-9
Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 901-10
Recalibration Schedule . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 901-12
NOVA-SENSOR OUTPUTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 901-12
0 to 20 mA Current Loop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 901-12
Relay Outputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 901-12
FINAL OPERATIONAL CHECK-OUT (CompTest™) . . . . . . . . . . . . . . . . . . . . . . 901-13
How to Start the CompTest . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 901-13
Entering the Safety-Code™ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 901-14
CompTest™Operational Sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . 901-14
MAINTENANCE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 901-15
Replacing the Infrared Gas Detection Electronics . . . . . . . . . . . . . . . . . . . . . 901-15
Digital Readout Module Replacement . . . . . . . . . . . . . . . . . . . . . . . . . . . 901-16
Spare Parts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 901-16
TROUBLESHOOTING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 901-16
Drifting/Shifting display . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 901-16
Digital Display reads approximately minus 12%LEL . . . . . . . . . . . . . . . . . . . 901-17
i June 2011 i

MODEL GIR901 INFRARED COMBUSTIBLE GAS
NOVA-SENSOR
QUICK START
Apply Power
A 30 second countdown is displayed, followed by a brief display of the firmware revision
(e.g. “1.18”). Then the decimal points will flash while the unit displays “000” to confirm
to the user that the NOVA-Sensor readout unit is properly functioning. This condition
remains during the remainder of the 6 minute warm-up period for the IR sensor head. If
“000” is not displayed within 6 minutes, and there is no background gas, the sensor
requires initial calibration.
Calibration
Wait at least 7 minutes after applying power before starting calibration. Calibration
requires a sample of the hydrocarbon gas you want to detect, mixed with air to a
concentration of 50% LEL (50% of the lower explosive limit of the gas). Insure that no
background gas is present before initiating calibration. Press the large MODE button on
the outside of the sensor housing for at least 10 seconds. The sensor flashes “000”
while sampling the zero gas condition (10 seconds). Apply 50% test gas when the 000
stops flashing and the countdown from 30 to 0 begins. Then “CAL” will be flashed as the
gas is sampled (may be as long as 3 minutes). When finished, the display reading will
start to increase - remove the gas now. The sensor will reset its calibration to read 50%,
and hold this reading for about 3 minutes. Normal operation begins once the displayed
level is safely below the LOW alarm setpoint.
Alarm Setpoints
To check the alarm setpoints without declassifying the area, simply press the large
external MODE button for 1 second. Each alarm setting will be displayed for 5 seconds,
along with its corresponding alarm LED (LOW or HIGH).To change setpoints, remove
housing cover to access buttons labeled “UP” and “DOWN”. Press the MODE button for
1 second, or press the UP/DOWN button. The LOW alarm LED will light as the setpoint
is displayed. Use the UP/DOWN button to alter the value. After 5 seconds, the HIGH
alarm LED and setpoint are displayed. Finally, after 5 seconds of button inactivity, the
sensor will return to normal operation.
DIP Switch: Latch/No Latch Setting for LOW Alarm Output
DIP switch position 4 (of the 4-position DIP) in the UP (Open) position selects LATCHING
mode for the LOW alarm. Placing the switch DOWN (Closed) configures the LOW alarm
as NON-LATCHING. Power must be cycled to “read” the new DIP setting.
!The HIGH alarm is always latched due to code requirements. DIP switch
positions 1, 2 and 3 are set at the factory - DO NOT change setting! If you
suspect that settings have been changed, reset per instructions on page
901-8.
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DESCRIPTION
The SST Model GIR901 Infrared Combustible Gas NOVA-Sensor is a completely self-
contained device that measures and displays the concentration of gas accumulated in a
protected area, performs local control functions, and transmits this information to a
central control point.
Principle of Operation
The GIR901 uses the absorption of hydrocarbons in the 3.3 μm to 3.5 μm range for the
detection of any hydrocarbon gas. The absorption of the hydrocarbon compounds is a
result of the oscillation of the H-C structure when exposed to energy. The GIR901 uses
an incandescent lamp pulsed at 4 Hz in conjunction with two piezoelectric light sensors
all contained in a stainless steel plug-in housing. In a patented configuration, the sensors
are close to each other and are exposed to the direct light from the lamp, with no mirrors
or other optical structures involved. In addition, almost no light is reflected by the walls of
the housing thus eliminating all possible influences from wall contamination. The active
sensor has an optical filter tuned to 3.4 μm; the reference sensor sees the wide-band
infrared signal from the lamp.
The presence of hydrocarbons will decrease the signal to the active sensor significantly,
while the signal to the reference sensor is almost unchanged. The electronics module
contained in the GIR901 constantly measures the signals from both sensors, averages
them to filter out noise and then calculates the ratio of the averaged active and reference
signals. With a constant length of the optical axis, the relation between the active/refer-
ence ratio and the actual gas concentration is logarithmic. The length of the optical path
yields an output for hydrocarbons that allows measurements with a resolution of 1%-2%
of reading. The ratiometric principle makes it possible to eliminate almost all effects of
temperature, aging, or fogging that would otherwise spoil the measurement. The optical
operation principle has the following advantages:
• Readings independent of Oxygen, wind, etc.
• Readings NOT influenced by cross-sensitivity and poisoning
• No burn-out, saturation, shift or drift when the detector is exposed to high gas
concentrations
Each SST NOVA-Sensor includes a high reliability microcontroller based transmitter/con-
troller in the associated explosion proof junction box. A digital read-out is provided to
continuously display operating status and the actual concentration of gas present in
percentage of the Lower Explosive Limit (%LEL). The transmitter converts this reading
to a standard 4-20 mA signal. This signal may be connected to a suitable SST NOVA-
5000 Gas Detection Module, or to any other device with a standard 4-20 mA input.
Connections between the transmitter and control device are normally made with 3
conductor cable [+24 VDC, 24 V return, 4-20 mA signal]. Dry contact relay outputs are
provided for low alarm, high alarm, and fault conditions. The low and high relays operate
at user adjustable alarm setpoints; the fault relay operates upon loss of power or internal
failure of the unit. Relays are suitable for controlling local HVAC or equipment shutdown.
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Detectable Gases
As a rule, most members of the hydrocarbon family are indiscriminately detected by the
GIR901. In contrast to the catalytic detector, long-chained hydrocarbons are detected
with greater sensitivity than Methane and Ethane. The measuring principle is similarly
applicable for other gases that chemically consist of dipole structures, such as CO2(with
a 4.25 μm filter), and others, but NOT to mono-atomic or bi-atomic elements, such as H2,
O2, CO, or He. See Tables 1 and 2.
TABLE 1
GIR901 Detectable gases
with sensitivity relative to Methane
Methanol . . . . . . . . . . . . .(10)
Propane . . . . . . . . . . . . (9.3)
Butane . . . . . . . . . . . . . (8.6)
Ethane . . . . . . . . . . . . . (8.0)
Diesel . . . . . . . . . . . . . (7.5)
Ethanol . . . . . . . . . . . . . (7.1)
Hexane . . . . . . . . . . . . . (5.8)
Octane . . . . . . . . . . . . . (5.7)
Iso-propanol . . . . . . . . . . . (3.4)
Pentane . . . . . . . . . . . . (2.5)
Methane . . . . . . . . . . . . (1.0)
Acetone . . . . . . . . . . . . (0.7)
Toluene . . . . . . . . . . . . . (0.5)
Ethene . . . . . . . . . . . . . (0.3)
For all gases with absorption lower than
Methane, special versions of the GIR901 have to
be used. The detector should always be
calibrated with 50% LEL Methane.
TABLE 2
Other gases that can not be detected
Carbon Disulfide . . . (no HC absorption)
Hydrogen . . . . . . (no HC absorption)
Ammonia . . . . . . (no HC absorption)
Ethene
Acetylene . . . (HC absorption at 3.05 μm)
Benzene . .(HC absorption below 3.30 μm)
Carbon Monoxide . . (absorption at 4.7 μm)
MODEL GIR901 INFRARED COMBUSTIBLE GAS NOVA-SENSOR
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TECHNICAL SPECIFICATIONS
Power Supply . . . . . . . . . . . .24 volts DC nominal, 180 mAstandby,
240 mA when in alarm. Will operate within
specifications at any supply voltage between 16
and 32 volts.
Range . . . . . . . . . . . . . . . .0 to 100% LEL Hydrocarbon
Start-up time . . . . . . . . . . . . .6 minutes operational
20 minutes to specification
Response time . . . . . . . . . . . .5 seconds typical. Time required for measured
concentration to reach one half of the final
concentration. Measured at 50% LEL.
Operating Temperature . . . . . . .-4 to +122oF. -20 to +50oC
Humidity . . . . . . . . . . . . . . .0-100% Relative Humidity
Signal Output . . . . . . . . . . . .0.16 mA output per %LEL
Automatically adjusted during calibration and
during CompTest™
Resolution . . . . . . . . . . . . . .2% LEL
Typical Combustible Gasses . . . .See Table 1
Relay Contact Ratings . . . . . . . .6 amps @ 28 VDC resistive
6 amps @ 300 VAC resistive
1/8 HP @ 120/240 VAC
Analog Output . . . . . . . . . . . .Sensor will source 0 to 20 mA DC into a load
of 600 ohms or less.
INSTALLATION
A complete GIR901 unit consists of an explosion-proof housing with MODE button,
Infrared gas sensor head, terminal blocks for field wiring and transparent lid used to
observe the operational status of the numerical readout and LED’s. The field wiring is
connected to the terminal blocks inside the enclosure. The terminal blocks are accessible
after removing the enclosure lid and the plug-in electronics module. The face plate on the
electronics module carries various displays and controls. These are:
• Three-digit LED readout to display of gas concentration and status.
• Four round LED’s, labeled “FAULT” (yellow), “HIGH” (red), “LOW” (red) and “CAL”
(green). These LED’s are used to signal alarms and operating modes.
• Two square pushbutton switches, labeled “UP” and “DOWN”. These switches are
accessible with a small screw driver or ball point pen and are used to adjust the
alarm trip points of the unit.
MODEL GIR901 INFRARED COMBUSTIBLE GAS NOVA-SENSOR
901-4 June 2011 901-4

Installation Sequence
The electronics module contains parts that are delicate and potentially sensitive to
electrostatic discharge (ESD). Remove the electronics module and store in the shipping
box during installation. Reinstall the module just before system start-up, after all drilling
and wiring is completed. The recommended installation procedure is as follows:
• Mount the enclosure
• Wire the power and signal cables
• Double check the field wiring for errors
• Set the DIP switches and suitcase jumpers on the electronics module
• Plug the electronics module into the housing
• Apply 24VDC power
• Set the alarm setpoints, if required
• Calibration and functional check out with CompTest, if required
Mounting the enclosure
The dimensions of the GIR901 are shown in the figure below. It is preferable to attach the
sensor to a wall or bracket, using bolts through the two mounting holes. However, these
mountings may be omitted if the electrical conduit is sufficiently rigid to support the weight
of the detector.
The location of the sensor is important. For lighter than air gasses, such as methane, the
sensor should be located above the spot where a leak is likely. For heavier than air
gasses, such as propane, locate the sensor below the expected leak. However, always
locate the sensors at least one foot (30.5 cm) above the floor to prevent damage from
water, dust, etc. Preferred orientation of thesensor is with the sensorhead pointing down,
as shown in figure 901-1. If necessary, it may be installed at an angle or horizontally.
Figure 901-1 Mounting Dimensions
MODEL GIR901 INFRARED COMBUSTIBLE GAS NOVA-SENSOR
901-5 June 2011 901-5

Wiring
Power input and Analog Signal Output
A typical installation is shown in figure 901-2. This setup uses three wires between the
NOVA-Sensor and the associated control modules. These wires carry the 24 VDC
operating power for the sensor, and transmit the 20 mAsignal to the controls. The wires
should be shielded or installed in metal conduit to prevent undesirable noise pickup. To
wire the NOVA-Sensor, carefully remove the electronics module from the housing by
pulling upward. Connect the three wires to the screw terminals in the housing as shown.
Note that the “24VRET” wire is the common return for DC power and the 4-20 mAsignal.
MODE Pushbutton and Remote RESET
The external MODE pushbutton on the NOVA-Sensor housing can be used to clear any
relays or alarms in the NOVA-Sensor which have been latched when activated. Pressing
the button for less than 3 seconds (0.5 second minimum) will cause the latched relays to
clear and the alarm setpoints to be momentarily displayed.
An optional external, remotely located, pushbutton can be wired to the terminal marked
RESET. This should be a normally open contact, and should connect the reset terminal
to 24VRET (common) to reset the sensor. The remote RESET button, when active for
between 0.5 and 3 seconds will clear any latched relays.
Relay Contacts
If the internal alarm and fault relay contacts are being used, additional wiring is required.
The terminals for the three relays are marked as shown in figure 901-3. Connect wires to
Figure 901-2 Typical Output Wiring
MODEL GIR901 INFRARED COMBUSTIBLE GAS NOVA-SENSOR
901-6 June 2011 901-6

the respective terminals for any
relays to be used. These are
voltage-free “dry” contacts for
connection to external equip-
ment. Each ofthe threecontacts
may be independently set to be
normally open or normally
closed. As shipped, the low and
high alarm relay contacts are
normally open, and will close
when an alarm condition is
detected. As shipped, the fault
contact will be closed under nor-
mal operating conditions, and
will open upon loss of power or
a fault in the NOVA-Sensor. The
sense of the relay contacts can
be changed by moving the
programming jumper plugs on
the bottom circuit board of the
electronics module.
• To change the HIGH
ALARM contact from normally open to normally closed, move the jumper on the
pins marked HI ALM from the NO to the NC pins.
• To change the LOW ALARM contact from normally open to normally closed, move
the jumper on the pins marked LO ALM from the NO to the NC pins.
• To change the FAULT contact from normally closed to normally open, move the
jumper on the pins marked FAULT from the OF (Open on Fault) pins to the CF
(Closed on Fault) pins.
!Relay contacts may require external protection to suppress transients. See
figure 901-5 and the section Relay Protection Circuitry below.
Remote Sensor Version
The remote sensor version is the same as a standard version, except that the sensor
head is located away from the electronics enclosure. A SST Model GIR900 Infrared
Combustible Gas Sensoris requiredfor usewiththe remoteGIR901 electronicspackage.
Asecond 3/4 inch conduit connection is provided to connectthe sensor electronics to the
remotely located sensor head.
Cableconsiderations
Four conductors are required between the Model GIR900 Sensor and the GIR901
electronics. These wires will be carrying a maximum of 20 mA at 24 volts DC to provide
the required operating current to the Infrared Sensor transmitter. In general, the length of
cable is not critical, as long asthetotal resistance ofthe cable doesnot exceed650 ohms.
It is important to use shielded cable, or to install the wires in metallic conduit. Excessive
noise picked up in the cables can make the display on the NOVA-Sensor jump between
various values and can make calibration impossible. This is because the noise makes
the NOVA-Sensor believe that the gas values are constantly changing. A constant gas
value is the criteria for the end of a calibration.
Figure 901-3 Relay Contact Connections
MODEL GIR901 INFRARED COMBUSTIBLE GAS NOVA-SENSOR
901-7 June 2011 901-7

• If shielded cable is used, it
must be grounded only at
the GND terminal in the
GIR901 electronics
enclosure. The GIR901
enclosure must also be
properly grounded. Insulate
the shield at the sensor end
so that it will not be
grounded.
• Avoid running the cable
close to high-powered
cables or equipment or close
to radio transmitters or an-
tennas.
Cable Color Codes
The GIR900 infrared gas sensor
head is supplied with five color
coded wires which connect to the
terminals in the GIR901 electronics package. See figure 901-4 for hookup. Be extremely
careful to connect each lead to the proper terminal. Interchanging two wires will almost
always result in a burned out sensor.
DIP Switch settings
One or two piano-type DIP switches are visible from the side of the electronics module.
These switches set the electronics for the type of sensor head installed, and set the
operating mode.
Four-Position DIP Switch
!WARNING: Switches 1, 2 and 3 are preset at the factory to DOWN/UP/UP
for switch positions 1, 2 and 3 respectively. DO NOT ADJUST these
switches! Serious damage to the sensor or electronics module may
occur if these switches are incorrectly set.
Switch position 4 selects the LOW alarm relay as latching or non-latching. The UP
position selects LATCHING mode: once activated, the low alarm relay will remain in the
alarm state until the NOVA-Sensor is manually reset with the MODE button or theremote
reset signal. The DOWN position selects NON-LATCHING mode: after activation, the low
alarm relay will return to the normal state as soon as the gas concentration sensed is less
than the low alarm set point. The HIGH alarm is always latched to conform to code
requirements.
Five-Position DIP Switch
This switch is provided on “low-power” models only. All five positions on this DIP switch
must be in the UP position to select the low-power mode. Any other setting will cause the
NOVA-Sensor to operate in standard power mode.
Figure 901-4 Sensor head color codes
MODEL GIR901 INFRARED COMBUSTIBLE GAS NOVA-SENSOR
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OPERATION
Power-Up
When power isfirst applied, the microcontroller executes abuilt-in test (BIT), duringwhich
various internal components and parameters are checked. During the BIT, the indicator
lights will be flashing. Upon successful completion of the BIT, the NOVA-Sensor begins
a 30 second countdown period to allow time for proper temperature stabilization. The
countdown is displayed on the digital read-out. At the end of the countdown, the
NOVA-Sensor displays its firmware revision code (e.g. “1.18”). The unit is now waiting for
the IR sensor head to warm up sufficiently to provide stable readings.
!Do not depress the large MODE button on the side of the enclosure during this
initial warm up period. Depressing the button during this time erases the
previously saved calibration data, and will make recalibration more difficult.
During warm up and normal operation, the digital read-out displays “000”. As a further
verification that the unit is operating properly, the decimal points on the digital read-out
slowly rotate from one digit to the next while displaying “000”). Three to five minutes after
the power was first applied, the NOVA-Sensor is operating at the factory default calibra-
tion and alarm setpoints. Calibration data and alarm setpoints are maintained in non-
volatile memory to insure proper operation should the +24 VDC supply be temporarily
interrupted. No special care is required to maintain this memory.
Changing the Setpoints
Setpoints for HIGH alarm and LOW alarm are available for user modification. Factory
defaults for the HIGH and LOW alarms are 50% LEL and 20% LEL.
!Setpoints will “roll over” to zero at 100% LEL.
Do not select setpoints below 5% LEL!
To adjust either the HIGH or LOW setpoints, momentarily press either the UP or DOWN
pushbutton on the face of the electronics module, using a small screwdriver or ballpoint
pen. At this point, the LOW alarm LED will turn on, and the LOW alarm setpoint will be
displayed. The user has 5 seconds to begin to adjust the LOW alarm setpoint by pressing
the UP or DOWN button. Once the microcontroller has detected 5 seconds of inactivity
(no button press), the unit will light the HIGH alarm LED and display the previously stored
setpoint value. The operator will again have 5 seconds to begin adjusting the HIGH alarm
setpoint. After an additional 5 seconds of inactivity, the NOVA-Sensor will store the new
values in non-volatile memory and return to normal operation.
MODEL GIR901 INFRARED COMBUSTIBLE GAS NOVA-SENSOR
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Calibration
The GIR901 NOVA-Sensor is pre-calibrated at the factory for a specific target gas. It
cannot be recalibrated to another hydrocarbon gas unless you replace the transmitter
module in the gas sensor head with a new module. See the markings on the outside of
the sensor head to determine which gas is required for calibration. A new calibration will
take care of changes in detector performance and drift. During the calibration procedure,
clean air as well as gas with a defined percentage of combustible gas are applied to the
detector in order to provide the NOVA-Sensor with reference points needed to measure
gas levels.
The presence of “clean” air, i.e. air without any combustible components, is absolutely
necessary to provide the electronics module with a reference point for 0% LEL gas
concentration. In locations where clean air cannot be assured, you may need to “purge”
the sensor with clean air from a gas bottle before starting the calibration procedure. DO
NOT USE nitrogen to purge the sensor, false readings may result!
The calibration can be performed by one person, and with the NOVA-Sensor operating
in the classified area. No manual adjustments are required for calibration.
!NOTE: The sensor must be calibrated using the gas that the sensor is
expected to detect at a concentration of exactly 50% of the lower explosive
limit (LEL) of the gas.
!The GIR901 must “warm up” for at least 7 minutes after power is first
applied before calibrating. Calibration will be more accurate if you can
wait 30 minutes before starting. Do not push the MODE button on the
housing during the first 10 seconds of warm up, or previous calibration
data will be erased from the non-volatile memory.
The calibration procedure is as follows:
1) Depress the large mode button on the side of the NOVA-Sensor enclosure and hold it
depressed for a full ten seconds. The NOVA-Sensor acknowledges by lighting the three
dots on the numerical readout.
!It isimportant to hold for 10 seconds to insure that the electronics in both
the IR sensor head and in the digital readout module are put into the
calibration mode.
2) Once the MODE button is released, the numerical readout will flash “000” and “...”
for about ten seconds. During this time, the NOVA-Sensor is storing the zero reference
point, based on clean air applied to the sensor.
3) The NOVA-Sensor then begins a 15-second count-down, during which it displays the
numbers “030” through “000” on the read-out. During this time, the NOVA-Sensor is
simply waiting for the calibration gas to be applied and conveyed to the sensor.
!In order to save gas it is recommended to apply calibration gas as soon as the
15-second count-down begins. Up to 3 minutes delay is tolerable for cases
where the sensor head is at a remote location and the calibration gas must be
applied through a long pipe.
MODEL GIR901 INFRARED COMBUSTIBLE GAS NOVA-SENSOR
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4) At this point, only the gas sensor head is being calibrated. During head calibration, the
output of the head is held at the “zero” level, so the digital read-out continues to alternate
between “CAL” and a small number that represents the zero gas concentration, relative
to the previous calibration. Additionally the CALLED blinks. This condition can last for up
to 5 minutes.
!If the digital readout begins to read the gas concentration at this point,
rather than remaining near zero, the MODE pushbutton was not held long
enough in step 1) above. In this case, remove gas, wait for sensor to return
to normal operation, then start again at step 1.
5) When the gas sensor head is successfully calibrated, the head output will be held
constant at the new calibration level, and the readout will start to count up from the
previous zero setting to the new calibration.
!IMPORTANT: The calibration gas should be removed from the sensor headas
soon as the display begins to count up. Leaving the gas on at this point will
result in wasted test gas.
6) When the read-out displays “050”, the new calibration reference for 50% LEL gas is
stored. At the same time the CAL LED changes from blinking to steady.
7) The 50% LELreading will be held for approximately 3 minutes, after which the read-out
will decrease. Once the read-out is below the LOW alarm setpoint or at zero, the
NOVA-Sensor returns to normal operation and the CAL LED is switched off. The
microcontroller in the NOVA-Sensor automatically stores the calibration in its internal
non-volatile memory for use in subsequent measurements.
During the calibration process, the 4-20 mA output is set to 2 mA and the relay outputs
are suppressed. The NOVA-Sensor automatically returns to normal operation when the
calibration is complete.
Failed or Incomplete Calibrations
If the calibration procedure is aborted (e.g. by not applying calibration gas), the NOVA-
Sensor will return to normal operation after a time-out period of 3 1/2 minutes. In this case
the NOVA-Sensor will use its original, pre-calibration data. Turning the power off will also
abort the calibration procedure. Common causes for incomplete calibration are:
1) Calibration gas runs out during calibration. In this case, wait for the NOVA-Sensor to
return to normal operation and repeat procedure with a fresh calibration gas bottle.
2) Calibration gas concentration too LOW. The NOVA-Sensor will not accept calibration
gas with concentration below 20% LEL. Using gas cylinders with low pressure will often
be interpreted by the NOVA-Sensor as low gas concentrations. In this case, wait for the
NOVA-Sensor to return to normal operation and repeat procedure with fresh calibration
gas bottle.
3) Gas applied at wrong time. Gas applied during step 2 above (too early, during clean
air sampling) will result in negative displays and inaccurate readings. If the gas is applied
too late (which may occur due to the pipe length when remote sensors are used) it may
not reach significant levels before the 3 1/2 minute time-out and thus abort the calibration
procedure.
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Recalibration Schedule
Due to the extreme stability of the infrared gas sensor, recalibration is rarely required.
However, SST recommends that test gas should be applied to the sensors every90 days
to verify proper sensor operation. Before testing, do a visual inspection to check for
contamination of the sintered metal sensor cover, loose parts, etc. Be sure to deactivate
any connectedequipment before applying test gasto thedetector to prevent falsealarms!
NOVA-SENSOR OUTPUTS
The characteristics of the various NOVA-Sensor outputs are explained in more detail in
the following sections.
0 to 20 mA Current Loop
The current loop output is normally between 4 and 20 mA, and is a direct linear read-out
of gas concentration. Output is 4 mAwhen no gas being detected. Output is 20 mAwhen
the full scale gas concentration of gas (100% LEL) is being detected. The 0 to 20 mA
circuitry will reliably and accurately (.002% typical nonlinearity) drive a load resistance of
between 100 and 600 ohms. The 0 to 20 mA circuitry is self calibrating and does not
require adjustment. The Safety Systems “Trim-Not” technology eliminates the require-
ment for field adjustable trim-pots.
Should a malfunction occur in the sensor or the current loop wiring, the output will, of
course, be 0 mA. Before any calibration has been performed, the output will be 2 mA.
During the start-up time delay and during routine calibrations, the output remains at 4mA.
During normal operation, the loop current can be determined with the following formula:
I (in mA) = 4 + 0.16 x %LEL
Relay Outputs
The NOVA-Sensor includes three(3) relays for connection to external devices. The LOW
alarm and HIGH alarmrelays operated whenthe concentration of gasmeasured exceeds
the respective setpoints. The fault relay transfers on detectionof a fault in theNOVA-Sen-
sor.
Each relay can provide either a normally open or normally closed dry contact output. The
LOW alarmrelay can be set aseither latchingor non-latching - seesection“DIP Switch
Settings”. The fault relay is always non-latching (self clearing).
Relay Protection Circuitry
Heavy duty relay contacts are provided in the NOVA-Sensor. These contacts are rated
for resistive loads. If used for switching inductive loads, such as relay coils, lamps,
beacons, etc., you must provide suitable suppression at the load. This will prevent
burning the relay contacts, and also suppress harmful transients which can affect the
operation of electronic equipment. See figure 901-5 for the recommended protection for
DC and AC loads.
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FINAL OPERATIONAL CHECK-OUT (CompTest™)
Once the NOVA-Sensor hasentered normal operation, afinal comprehensive outputtest
(CompTest)of all detector inputs and outputs is available. TheCompTest isa waytoverify
that the NOVA-Sensor relay outputs and 0 to 20 mAcurrent loop are correctly operating.
It can also be used to determine if the peripheral equipment is properly connected to the
NOVA-Sensor.
The CompTest ramps the 0 to 20 mA current loop through each of its assigned values
while changing the relay outputs as well. Each output state for the 0 to 20 mA loop and
each of the three relays is held for about 2 seconds and repeated 3 times. The test lasts
for approximately 1 minute. At the completion of the test, the built-in test (BIT) is executed
and the unit is returned to normal PROTECTIVE MODE operation.
What keeps the CompTest from occurring during operation or by mistake?
BecausetheCompTestexercisesalloutputs,includingLOWALARM andHIGHALARM
states, there are several built-in safe guards against its inadvertent use. The button
located on the side of the NOVA-Sensor (the Mode button) will not initiate a CompTest.
The remote reset input on the NOVA-Sensor is used to initiate the test, based on a coded
sequence of ON’s and OFF’s. Upon receiving the proper coded input (the CompTest
Safety Code), the NOVA-Sensor begins the test. The NOVA-Sensor will only start the
output tests if the proper Safety Code is entered. For additional security against inadver-
tent use, the Safety Code can only be entered during the first 6 minutes after the
NOVA-Sensor has been returned to normal operation. Requiring a special Safety Code
to be entered within 6 minutes of applying power limits the CompTest to authorized
personnel during system commissioning and periodic inspections.
How to Start the CompTest
!WARNING: Do not execute the CompTest until verifying that all systems
connected to the NOVA-Sensor are properly configured to execute a test.
Failure to do so may result in an unnecessary release of fire extinguishant or
unnecessary dispatching of emergency personnel.
Figure 901-5 Relay Contact Protection Scheme
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The CompTest must be started within 6 minutes of entering Protection Mode. The
Safety-Code™ is entered into the NOVA-Sensor by using the remote Reset button, not
the MODE switch which is on the NOVA-Sensor housing.
You begin the test in either of the two ways described below.
To begin the Test if Power has just been applied
To begin the test wait at least 3 minutes after power up (but not more that 6 minutes).
Then enter the Safety-Code™as described below.
To begin the test in an already operational system
It is not necessary to remove and reapply system power to initiate entry to Protection
Mode. If the NOVA-Sensor is already powered up and in Protection Mode, press the
Sensor Reset Button and hold it in (active) for 20 to 30 seconds, then release it. This
causes the sensor to begin the normal power up sequence (as if power had beencycled).
Wait for 5 seconds after releasing Reset, then enter the Safety-Code asdescribed in the
following section.
Entering the Safety-Code™
After followingtheprevious instructions toinsurethat theNOVA-Sensorisreadytoaccept
the Safety Code, press the Reset Button for three (3) ON cycles (5 to 10 seconds each,
separated by 5 to 10 second pauses). This will cause the sensor to execute the
CompTest™. The sequence is summarized as follows:
Action Position: Hold For Duration of:
1ON 5 Seconds
2 OFF 5 Seconds
3ON 5 Seconds
4 OFF 5 Seconds
5ON 5 Seconds
6OFF
Upon accepting the Safety Code, the NOVA-Sensor will pause for 10 seconds and begin
the CompTest.
If an incorrect code is entered, the NOVA-Sensor will pause 15 seconds and initiate a
normal reset sequence prior to returning to normal operation.
CompTest™Operational Sequence
Upon receipt of the Safety Code within the first 6 minutes of entering Protection Mode,
the following sequence is executed:
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Fault Test
The following outputs are simultaneously toggled three (3) times, and are held in each
state for approximately 2 seconds.
0 to 20 mALoop Alternates between 0 and 4 mA
Fault Relay Toggles between Fault and nofault
LOW alarm relay Inactive
HIGH alarm relay Inactive
LOW Alarm Test
The following outputs are simultaneously toggled three (3) times, and are held in each
state for approximately 2 seconds.
0 to 20 mALoop Alternates between 4 and 12 mA
Fault Relay In Fault
LOW alarm Relay Toggles between active and inactive
HIGH alarm Inactive
HIGH Alarm Test
The following outputs are simultaneously toggled three (3) times, and are held in each
state for approximately 2 seconds.
0 to 20 mALoop Alternates between 4 and 20 mA
Fault Relay In Fault
LOW alarm Relay Inactive
HIGH alarm Relay Toggles between active and inactive
Upon completion of the CompTest, the built-in test (BIT) is executed and the system then
returns to normal operation. If desired, the output test can be repeated by again entering
the CompTest security code.
MAINTENANCE
The GIR901 is easy to service. Most service activities will require the lid of the detector
base or the enclosure of the GIR900 sensor head to be opened.
!CAUTION: Before opening lids or enclosures, the area must be free of
any combustible gasses!
Replacing the Infrared Gas Detection Electronics
After many years of use, the infrared source lamp in the detection electronics may fail. In
this failure mode, the digital readout will display approximately “-12”, and there will be
no response when gas is applied to the gas detector. To replace, follow this procedure:
1) Remove the window cover from the NOVA-Sensor readout module and unplug the
electronics module. This will disconnect the power to the IR sensor head.
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2) Remove the sintered metal cover from the sensor head by loosening the set screw and
then turning the cover counter-clockwise.
3) The infrared source lamp is contained inside the plug-in gas detection element visible
on the PC board assembly. Grasp the detection element and lift it (along with the PC
board assembly) from the housing. Replace with a new Infrared Transmitter Module
available from SST.
4) Line up the two connectors on the bottom of the infrared transmitter module with the
mates inside the housing and plug in. Replace the sensor head cover and tighten set
screw.
5) Replace the digital readout electronics into the housing.
!Do not depress the MODE button on the side ofthe enclosure during this
initial warm up period. Depressing the button during this time erases
previously saved calibration data, and will make recalibration more
difficult.
6) Complete the calibration of the new electronics, following all instructions listed under
Calibration in this manual.
Digital Readout Module Replacement
If the electronics module with digital readout ever has to be replaced, the new module
must be calibrated to the sensor head installed on the enclosure.
Spare Parts
Installations which require on-site spare parts inventory should order the following part
numbers:
40901-02 . . . . . . . Combustible Electronics Module with digital readout
40901-35-2 . . . . . . . Plug-in Transmitter Module, Methane
40901-35-3 . . . . . . . Plug-in Transmitter Module, Propane
40901-35-5 . . . . . . . Plug-in Transmitter Module, Butane
40901-35-7 . . . . . . . Plug-in Transmitter Module, Ethane
40901-35-8 . . . . . . . Plug-in Transmitter Module, Pentane
TROUBLESHOOTING
Drifting/Shifting display
Drifting or shifting or otherwise unexplainable display (i.e. display of negative or positive
gas values with no apparent cause) on GIR901 Infrared NOVA-Sensors can have the
following causes:
1) Bad contact between electronics module and terminal blocks in enclosure. This
effect is noticeable when pressing on the installed electronics module from the top
or when twisting it.
2) Loosened or contaminated suitcase jumper on relay board of electronics module.
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