PureAire Monitoring Systems Air Check EX ST-46 User manual
PureAire Monitoring Systems, Inc. 10/25/07
1
Welcome to PureAire Monitoring Systems
I’d like to thank you for investing in our continuous life safety and process control toxic gas
monitoring systems.
PureAire offers an unbeatable combination of experience and innovation in solving the safety
and environmental needs of our customers. We’re capable of providing small systems of a few
points to a total multi-point turnkey computerized package.
PureAire’s proprietary sensor cell technology and state-of-the-art electronics are designed to
interface with the latest digital or PLC based control systems. We believe that our experience,
innovative products and commitment to service will satisfy your specific monitoring needs now
and in the future.
Our growth is a result of our total commitment to supporting our customers. We’re available 24
hours a day, 7 days a week to help you when you need us. Our 24-hour Emergency phone
number is 1-224-443-5445. We can provide field service, preventative maintenance programs
and training to your technicians in the operation of our equipment. Our goal is to provide the
best after sale service and support in the industry. That’s just one way PureAire takes that extra
step to ensure your complete satisfaction.
Thank you again for investing in PureAire Monitoring Systems for your monitoring needs and
I’m proud to welcome you to our family of valued and satisfied customers.
Sincerely,
Albert A. Carrino
President
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Table of Contents
1: Introduction........................................................................................................ 4
1.1 Component Identification .......................................................................... 5
1.1.1 Front Panel....................................................................................... 6
1.1.2 Overall ............................................................................................. 6
1.1.3 Gas Sensor ....................................................................................... 6
2: Specifications..................................................................................................... 7
2.1 Performance Specifications ....................................................................... 7
2.2 Gas Detection Systems .............................................................................. 7
2.3 Signal Outputs ........................................................................................... 7
2.4 Electrical Requirements............................................................................. 7
2.5 Physical Characteristics ............................................................................. 7
2.6 Safety Characteristics ................................................................................ 8
3: Installation ......................................................................................................... 9
3.1 Mounting.................................................................................................... 9
3.2 Electrical.................................................................................................... 9
3.3 Optional Outputs...................................................................................... 10
3.3.1 Isolated 4-20 mA ........................................................................... 10
3.3.2 Modbus RS-485 Serial................................................................... 11
3.3.3 Alarm Relays ................................................................................. 12
4: Normal Operation ............................................................................................ 13
4.1 Power Up Delay....................................................................................... 13
4.1.1 Sensor Poisoning..................................................................... 13
4.2 Concentration Display ............................................................................. 13
4.3 Analog Output ......................................................................................... 13
4.4 Fault Alarm.............................................................................................. 13
4.5 Concentration Alarms.............................................................................. 13
4.6 Alarm Reset ............................................................................................. 14
4.7 Loss of Power Indication ......................................................................... 14
4.8 Routine Maintenance Schedule ............................................................... 15
4.8.1 Routine Visual Checks .................................................................. 15
4.8.2 Recommended Routine Maintenance Schedule ............................ 15
5: Maintenance & Calibration.............................................................................. 16
5.1 Sensor Calibration ................................................................................... 16
5.1.1 Optional Calibration Equipment.................................................... 16
5.1.2 Entering the Calibration Mode ...................................................... 16
5.1.3 Zero Calibration............................................................................. 16
5.1.4 Span Calibration direct from cylinder gas .................................... 17
5.1.5 Displaying Zero/Gain Settings ...................................................... 18
6: Diagrams & Schematics .................................................................................. 19
6.1 Dimensional Drawing.............................................................................. 19
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7: Appendix ......................................................................................................... 20
7.1 Modbus RS-485 Serial Interface.............................................................. 20
7.1.1 RTU Address ................................................................................. 20
7.1.2 Modbus Data Registers and Function Codes................................. 20
7.1.3 Modbus Configuration Software ................................................... 22
7.2 Alarm Relays .......................................................................................... 23
7.2.1 Alarm 3 (Sensor Fault Alarm) .............................................................. 23
7.2.2 Alarm 1 and Alarm 2 (Concentration Alarms) ..................................... 23
7.2.3 Alarm Relay Configuration .................................................................. 24
7.3 Connecting Remote Digital Display…………………………………….25
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1: Introduction
The Air Check EX is an explosion-proof toxic gas monitoring system
designed for the continuous detection and measurement of toxic gas leaks. It is a
single point monitoring system housed in an explosion-proof enclosure. The
enclosure is suitable for use in Class 1, Group B, C, D and Class 2, Group E, F,
and G hazardous areas.
NOTE: Acetylene monitor enclosure is special and rated for Group A
The system has the following features:
Explosion-proof transmitter enclosure
Non-intrusive, one-man calibration
Local digital display
4-20 mA output
Supervised sensor cell
24 VDC operation
A variety of output options (isolated analog output, Modbus, alarm relays)
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1.1 Component Identification
1.1.1 Front Panel
Digital Display — A 3½ digit LCD which continuously displays the measured
gas concentration value when in the normal monitoring mode. Displays zero and
span values when in the Calibration mode. Target gas and unit of measure appear
adjacent to the digital display.
Left Indicator Arrow — Unlit during normal operation. Lit continuously when
in the Calibration mode, flashes (slow) during power up and calibration delay
periods, flashes (fast) when an over-range condition is detected.
Fault/Keypad LED — This key is used as a dual-purpose indicator. It
momentarily lights to provide visual feedback that the magnetic key is being
activated. It also flashes once per second, without a magnet near the keypad, to
signal a Fault condition.
Cal Key — A magnetic key used to place the instrument in the Calibration
mode.
Span Adjustment Keys — Magnetic keys used to adjust the instrument’s span
(gain) up/down when in the Calibration mode. Display current gain setting when
touched with a magnet during normal operation.
Zero Adjustment Keys — Magnetic keys used to adjust the instruments zero
up/down when in the Calibration mode. Display current span adjustment when
touched with a magnet during normal operation.
Unity Key — Used for calibration when a new LEL sensor is installed. When a
new LEL sensor is replaced, selecting the Unity key will center both the zero and
span pots. For more information consult PureAire.
Digital Display
Left Indicator
Arrow
Calibration Key
(magnetic)
Reset Key
(magnetic)
Span and Zero
Adjustment Keys
(magnetic)
Fault / Keypad
LED
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1.1.2 Overall
Explosion-Proof Housing — Meets requirements for installation in Class 1,
Group B, C, and D and Class 2, Group E, F, and G hazardous areas. Magnetic
keypad permits calibration without declassifying area.
Front Panel — Incorporates local digital display, magnetic keys, etc. See 1.1.1
above for front panel component details.
Sensor / Sensor Cover — Renewable, plug-in electrochemical sensor with
threaded cover.
1.1.3 Gas Sensor
LEL Sensor — This is a disposable cell that has an operational life of
approximately 4 to 5 years.
IMPORTANT: Be sure to classify the area as non-hazardous prior to
Opening the ST-46A or any other electronic
enclosures.
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2: Specifications
2.1 Performance Specifications
Sensor Type: Disposable, LEL catalytic bead
Response Time: Within 30 seconds to T90.
Repeatability: ±10% of full scale.
Operating Temperature: 14° to 113°F (0° to +40°C); consult PureAire for lower operating temperatures.
Humidity: Typically 5 to 95% RH.
2.2 Gas Detection System
Type: Proprietary catalytic bead.
Sensor Life: 4 to 5 years under normal conditions.
Detectable Gases: Combustible Gases:
Acetylene
Methane (CH4)
Gasoline
Hexane
Propane
Hydrogen
IPA
2.3 Signal Outputs
Local Display: 3-1/2 digit LCD
Analog Output: 4-20 mA; isolated 4-20 mA output optional
Serial Output: Optional Modbus RS-485 serial interface
Alarm Relays: Optional SPDT High, Warning, and Fault alarm relays
2.4 Electrical Requirements
Power: 19-48 VDC; less than 4 watts. (200mA)
2.5 Physical Characteristics
Dimensions: 5.50 (W) x 10.6 (H) x 4.55 (D) inches.
Weight: Approximately 6 pounds.
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2.6 Safety Characteristics
Transmitter enclosure suitable for Class 1, Group B, C, D and Class 2, Group E, F, and G hazardous
areas. Also meets NEMA 4 with included O-ring.
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3: Installation
3.1 Mounting
The Air Check EX monitoring system is packaged in an explosion-proof
housing with three ¾ inch NPT conduit hubs.
The system should be mounted on a vibration-free surface and out of direct
sunlight. The sensor should facing toward the ground.
3.2 Electrical
The Air Check EX is a 3-wire device. There is a positive 24 VDC power wire
and a positive output signal wire, which is typically 4-20 mA. The third wire is
system common and serves as power supply and signal returns. These connect to
the three point terminal block labels TB2. An earth ground lug inside the
enclosure is provided for earth grounding of shied wires.
PureAire recommends the use of a General Cable #E2203S.30.86 or equivalent
for analog output and 24 VDC power input. The maximum permissible cable
length is 0.62 miles (1 km).
PC Board for LEL catalytic sensors
TB1
LEL catalytic
sen
sor cell
Compensator,
Common and
Detector
Connections
TB2
Power,
Signal Out, and
Ground
Connections
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3.3 Optional Outputs
NOTE: The Air Check
EX may be configured with one of the following
optional outputs isolated 4-20 mA, Modbus serial output, SPDT alarm relays.
Optional outputs are provided using an auxiliary, factory-installed electronics
board. The instrument can only accommodate one optional output.
3.3.1 Isolated 4-20 mA
An optional isolated 4-20 mA output board is available. A 2-point terminal strip
(TB1) provides the 1500 V isolated 4-20 mA output signal.
TB1
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3.3.2 Modbus RS-485 Serial Interface
The Modbus RS-485 Serial Interface board allows up to 128 Air Check EX
gas monitors to communicate to a Modbus master device on a single cable. The
gas detector functions as a slave device; a PLC or PC running MMI or BUI
software equipped with a Modbus driver functions as the master.
The RS-485 standard allows cable lengths up to 4000 feet between the Modbus
master and slave. Both 4-wire full duplex and 2-wire half duplex connections are
supported by the Modbus RS-485 serial interface option.
NOTE: See Appendix for RTU address, Registers, and Function Code
information.
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3.3.3 Alarm Relays
The alarm option provides 5-amp resistive form C relays for Alarm 1, Alarm 2,
and Alarm 3 conditions. They may be wired for either normally open or normally
closed operation.
IMPORTANT: The relay contacts are rated for 5 amp resistive loads.
Appropriate surge suppressors should be installed across loads to prevent arcing
on the contacts. Arcing generates high levels of RFI that may interfere with
measurement signals.
The alarm relay PCB also incorporates a remote reset switch (TB4) for use if the
alarm relays are configured for latching operation (see Appendix).
These alarms are factory-set as follows:
Alarm 1 — 20% LEL, non-latching.
Alarm 2 — 40% LEL, latching.
Alarm 3 — This is a fail-safe Fault relay and is activated when a sensor fault,
such as a missing sensor, is detected. It also indicates loss of power conditions.
NOTE: Alarm 1 and 2 setpoints and operation (latching/non-latching/fail-safe)
are user-adjustable. See the Appendix for more information.
Alarm Relay
Terminals
TB4 — Remote Alarm
Reset Connection
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4: Normal Operation
The Air Check EX is a single point monitoring system designed for the
continuous detection and measurement of toxic gas leaks.
4.1 Power Up Delay
The Air Check EX incorporates a power up delay that holds the analog output
at 4 mA for one minute after power is applied. This allows the sensor to stabilize
and reduces the possibility of triggering an erroneous alarm.
4.1.1 Sensor Poisoning
It is important to understand that all catalytic sensors may be poisoned, causing
loss of sensitivity. Silicon, sulfur and lead containing compounds are especially
detrimental. All combustible gas detectors operating in these environments
should be calibrated more frequently.
4.2 Concentration Display
This is a real time display of the measured concentration of the target gas. The
concentration value appears on the LCD; the target gas and unit of measure
(PPM, PPB, etc.) are indicated adjacent to the digital display.
When the instrument is in the normal monitoring mode, the left arrow indicator
on the LCD will be “off.” Should the measured concentration exceed the range of
the instrument however, the left arrow indicator will flash rapidly and three
horizontal dashes (- - -) will appear on the LCD.
4.3 Analog Output
During normal operation, outputs an analog signal directly proportional to the
measured gas concentration, with 4 mA being “0” and 20 mA being full scale.
4.4 Fault Alarm
The Air Check EX features a self-supervised gas sensing system which alerts
the operator to sensor faults, such as a missing sensor, or negative drift. In the
event a sensor fault is detected, the analog output will drop to 0 mA, FLt will
appear on the local digital readout, and the red Keypad/Fault LED will flash at
one second intervals. If the instrument is configured with the alarm relay option,
the Alarm 3 (Fault) relay will also be activated.
4.5 Concentration Alarms
If the Air Check EX is equipped with the Alarm Relay option, the appropriate
Alarm 1 or Alarm 2 relay will activate when the measured gas concentration
exceeds the alarm setpoint.
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4.6 Alarm Reset
If the instrument is equipped with the Alarm Relays option and one or more
alarms are configured for latching operation (see Appendix), alarm conditions
must be acknowledged by manually resetting the alarm. This manual alarm reset
may be performed remotely via a control room signal or locally by holding the
magnet at about the 7 o’clock position on the base of the cover assembly.
4.7 Loss of Power Indication
In the event the Air Check EX loses VDC power, the local display go blank
and the 4-20 mA analog output signal will drop to 0. If the instrument is
configured with the optional Fault Alarm Relay, that relay will de-energize.
On units equipped with the
Alarm Relays option, alarm
conditions are reset /
ackno
wledged by holding the
magnet at the base of the
cover assembly at about the
7 o’clock position.
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4.8 Routine Maintenance Schedule
Continuous gas detection systems depended upon to measure and detect
hazardous gas leaks in the workplace require periodic maintenance to ensure
proper operation. The frequency with which this routine maintenance is required
depends on the environment, since temperature, humidity, gas concentrations,
and dust all affect system operation.
The following tables are intended to serve as general guidelines for routine
maintenance. The conditions in your particular application, as well as your
organization’s maintenance policies, will ultimately determine the best routine
maintenance schedule for your equipment.
4.8.1 Routine Visual Checks
Item Status With No Gas Present
Local Display Display should read “0.0” (“0” for LEL gases)
Fault Keypad LED Should not be illuminated
4-20 mA Output Output should be 4 mA
Gas Concentration
Alarm Relays (optional) De-energized
System Fault Relay
(optional) Energized
4.8.2 Recommended Routine Maintenance Schedule
Routine Visual Checks Monthly
Sensor Calibration Every 6 months
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5: Maintenance & Calibration
Maintenance and calibration should be performed only by qualified personnel.
5.1 Sensor Calibration
The Air Check EX system requires periodic calibration with the appropriate
standard gas. Calibration should be performed whenever 6 to 12 months has
passed.
5.1.1 Optional Calibration Equipment
The following equipment is available from PureAire to facilitate gas calibration:
Part Number Description Quantity
6D360248 ** Span Gas, specify gas 50% LEL in Air 1 btl 103 liters
CZF7R000255 ** 715 Regulator 500cc/min flow 1 ea.
83505 Calibration Cap for LEL Sensor Cell 1 ea.
** Contact Calgas Div of Air Liquide Ph: 800-638-1197
5.1.2 Entering the Calibration Mode
The Air Check EX features a magnetic keypad, which permits one-man, non-
intrusive calibration. All zero and span adjustments can be made without
removing the cover of the enclosure housing.
To place the instrument in the Calibration mode, briefly hold the magnet over the
CAL key located on the lower left of the front panel. The left indicator arrow on
the upper left side of the LCD will light and the 4-20 mA signal will hold at 1.5
mA, indicating that the instrument is in the Calibration mode.
5.1.3 Zero Calibration
IMPORTANT: This procedure should be performed under normal monitoring
conditions, without any of the target gas present.
1. Check the instrument’s gas concentration reading on the local display.
2. If the display does not read a steady “0,” hold the magnet over the UP ZERO
or DOWN ZERO keys and adjust the reading for the correct zero value.
CAL Key
(magnetic)
Span and Zero
Adjustment Keys
(magnetic)
Left Indicator
Arrow
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5.1.4 Span Calibration from span gas cylinders
CAUTION: Be sure to observe all safety guidelines when generating and using
calibration gases.
Connect p/n 690100 calibration cap to the LEL sensor cell.
IMPORTANT: Be sure to perform the calibration with certified span gas
and within the recommended use date. PureAire recommends that you verify
that the concentration of the calibration gas is the same after calibration as
it was before.
1. Connect the calibration cap to the LEL sensor.
2. Open the regulator valve on the span gas cylinder and expose the sensor cell
to the span gas for 1 to 2 minutes until the gas reading stabilizes.
3. If the correct gas concentration is not displayed; With the left indicator arrow
still lit, Hold the magnet over the UP SPAN or DOWN SPAN key and adjust
the display reading for the correct value.
NOTE: For calibrating Gasoline using Hexane, hexane has a low vapor
pressure and the sensor cell will continuously rise, therefore only expose the cell
to a flow rate of 200cc/min for 1-2 minutes and then adjust the span to the
calibration standard. If the cell is exposed to higher flow rates the system will
rise too quickly and make it difficult to adjust the span.
4. Close the regulator valve on the span gas cylinder and remove from the inlet
of the calibration cap. Remove calibration cap from the sensor cell by gently
rocking the cap as you pull downward. Permit the instrument to return to a
zero reading.
5. Allow the instrument to return to a zero reading If the instrument has not
returned to zero after 3 minutes readjust the zero as required by repeating the
procedure outlined in section 5.3.4.
6. Exit the Calibration mode by touching the magnet to the CAL key. The
instrument will return to normal operation after a one-minute delay.
NOTE: If the CAL mode is not exited manually, it will exit automatically after
five minutes of inactivity.
Calibration Cap
PureAire p/n 83505
Re
gulator, Model 715
500 cc per minute flow
p/n CZF7R000255
Order from C
algas/
Air Liquide
Calibration gas
Methane 50%
LEL
p/n 6D360248
Order from Calgas/
Air Liquide
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5.1.5 Displaying Zero / Gain Settings
The Zero and Span values applied during calibration may be read on the front
panel of the LCD after exiting the Calibration mode. These values provide an
indication of how much sensor sensitivity has declined over time — the higher
the gain, the greater the degree of sensor sensitivity deterioration.
These values are displayed as follows:
1. Exit the Calibration mode and wait for the one minute delay to end (the left
indicator arrow will stop flashing and remain unlit).
2. Hold the magnet over the UP SPAN key. The amount of zero offset, in
percent of full-scale, will be displayed.
3. Hold the magnet over the DOWN SPAN key. The amount of gain applied
will be displayed. This value will range between 0.5 and 2.0.
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6: Diagrams & Schematics
6.1 Dimensional Drawing
LEL catalytic
sensor cell
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