MODEL: SO 2-100ppm. Optional 20ppm and 10ppm
Available in: 24Vdc Version / 12Vdc Version / 10 - 32Vdc
ASSEMBLY CONSISTS OF:
XP-SO2 housing (supersedes PE-EX-SO2)
ST1300-XXX sensor (supersedes PE1300-24-20)
JB2 junction box
CB2 connector board
ELECTROCHEMICAL SO2 DETECTOR
(Used with ST1300 SO2 Sensor)
Part Number: MAN-0027-00 Rev 1
This manual is provided for informational purposes only. Although the information contained in this
manual is believed to be accurate, it could include technical inaccuracies or typographical errors.
Changes are, therefore, periodically made to the information within this document and incorporated
without notice into subsequent revisions of the manual. Net Safety Monitoring Inc assumes no
responsibility for any errors that may be contained within this manual.
This manual is a guide for the use of a Toxic Gas Transmitter and the data and procedures contained within
this document have been verified and are believed to be adequate for the intended use of the transmitter. If the
transmitter or procedures are used for purposes other than as described in the manual without receiving prior
confirmation of validity or suitability, Net Safety Monitoring Inc does not guarantee the results and assumes
no obligation or liability.
No part of this manual may be copied, disseminated or distributed without the express written consent of Net
Safety Monitoring Inc
Net Safety Monitoring Inc products, are carefully designed and manufactured from high quality components
and can be expected to provide many years of trouble free service. Each product is thoroughly tested,
inspected and calibrated prior to shipment. Failures can occur which are beyond the control of the
manufacturer. Failures can be minimized by adhering to the operating and maintenance instructions herein.
Where the absolute greatest of reliability is required, redundancy should be designed into the system.
Net Safety Monitoring Inc, warrants its sensors and detectors against defective parts and workmanship for a
period of 24 months from date of purchase and other electronic assemblies for 36 months from date of
purchase.
No other warranties or liability, expressed or implied, will be honored by Net Safety Monitoring INC
Contact Net Safety Monitoring Inc or an authorized distributor for details.
2
Table of Contents
DESCRIPTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
FEATURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
SPECIFICATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
SENSOR OPERATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
SENSING ELEMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Table 1 - % Cross Sensitivity of Electrochemical Sensor
to Other Gases (SO 2 = 100%) . . . . . . . . . . . . . . . . . . . .
SENSOR OUTPUT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
INSTALLATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
DETECTOR POSITIONING . . . . . . . . . . . . . . . . . . . . . . . .
W IRING REQUIREMENTS . . . . . . . . . . . . . . . . . . . . . . . . .
Table 2 - Maximum W iring Distances . . . . . . . . . . . . . . .
Sensor to Controller/Transm itter . . . . . . . . . . . . . . . . . . . . .
SENSOR W IRING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
START-UP PROCEDURE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
CALIBRATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
MAINTENANCE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
SENSING ELEMENT REPLACEMENT . . . . . . . . . . . . . . . .
TROUBLESHOOTING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Table 3 - Troubleshooting Guide . . . . . . . . . . . . . . . . . .
APPENDIX A Electrostatic Sensitive Device Handling Procedure .
APPENDIX B W ire Resistance In Ohm s . . . . . . . . . . . . . . . . . . . .
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11
DESCRIPTION
The Net Safety Monitoring Inc. SO 2-100 Electrochem ical SO 2 Detector consists of an explosion-proof
enclosure, which contains sensor electronic circuitry and an electrochem ical SO 2 sensing elem ent. This
SO 2 sensor provides continuous m onitoring of sulphur dioxide (SO 2) concentrations in the range of 0 to
100 parts per m illion (PPM) (optional 10 and 20 PPM). The sensor can be used with one of the Net Safety
Monitoring Inc. Uni-Trol™ Controllers or Display Modules, or it can be used with other devices that are
capable of m onitoring a 4 to 20 m A dc input and allow for calibration. The explosion-proof sensor is CSA
certified for hazardous locations for Class 1, Division 1, Groups C and D.
FEATURES
<
<
<
<
<
<
Electrochem ical sensor for increased accuracy and reliability.
High specificity to SO 2 reduces the chance of false alarm s resulting from the presence of other gasses.
Tem perature com pensation to ensure consistent perform ance over the entire operating tem perature
range.
Self-contained transm itter circuitry perm its use without a separate transm itter.
Explosion-proof housing.
EMI/RFI hardening.
Figure 1 - SO2 Detetctor Assembly
1
SPECIFICATIONS
<
Operating Range:
0 to 10, 20 and 100 ppm .
<
Response Time:
T90 response tim e <20 sec.
<
Drift:
Less than 2 ppm per m onth.
<
Accuracy:
±10 percent of applied gas concentration or ±3 ppm , whichever is greater.
<
Sensor Life:
Com m only 2 to 3 years.
<
Operating Voltage:
10 to 32Vdc. 24Vdc nom inal.
Optional 12Vdc m odel available.
<
Temperature Range:
Continuous Operation:
-20ºC to +50ºC (-4ºF to +122ºF).
Recom mended Storage:
0ºC to +20ºC (+32ºF to +68ºF).
<
Hum idity Range:
Continuous: 15 to 90% RH, non-condensing.
Intermittent:
0 to 90% RH, non-condensing.
Storage: 15 to 90% RH, non-condensing.
<
Enclosure M aterial:
Anodized alum inum .
<
Dimensions:
2.60 inches (6.6 cm ) in width.
5.55 inches (14.1 cm ) in length.
Refer to Figure 1.
<
Shipping W eight (approximate) :
Aluminum Housing :
Sensing elem ent :
2.5 pounds (1.1 kilogram s).
0.2 pounds (0.1 kilogram s).
2
SENSOR OPERATION
SENSING ELEM ENT
The electrochem ical sensing elem ent uses capillary diffusion barrier technology for detecting the presence
of sulphur dioxide (SO2) gas. The electrochem ical sensing elem ent provides im proved accuracy and
reliability, as well as extended calibration intervals when com pared to ordinary solid state type sensors.
The response of the sensing elem ent is highly specific to SO 2. Since m any com m only encountered gases
have little, if any, effect on the electrical response of the sensor, false indications caused by the presence
of these gasses is greatly reduced. Below is a list of cross sensitivity of the electrochem ical sensor to
various other gases.
Table 1 - % Cross Sensitivity of Electrochemical Sensor
to Other Gases (SO2 = 100%)
0%
10%
60%
-60%
125%
-125%
CO
HCL
HCN
CL 2
H 2S
NO 2
NO
H2
C 2H 4
SENSOR OUTPUT
The sensor housing contains the circuitry for generating a 4 to 20 m A dc output signal, corresponding to
levels of SO 2 from 0 to 100 PPM (optional 10 and 20 PPM). The 4 to 20 m A output is an un-calibrated
signal. Therefore, calibration capabilities m ust be provided by a transm itter, controller, or display m odule,
to be used with the sensor.
INSTALLATION
CAUTION:
The electrochemical sensor contains semiconductor devices that are sensitive to electrostatic
discharge. Handle the device by the housing, taking care not to touch electronic components or
term inals. Refer to 'Electrostatic Sensitive Device Handling Procedure' in the Appendix for further
details.
DETECTOR POSITIONING
Proper detector positioning is essential for providing m axim um protection. The m ost effective num ber and
placem ent of sensors varies depending on the conditions at the job site. The individual perform ing the
installation m ust rely on experience and com m on sense to determ ine the num ber of detectors needed and
the best detector location.
The following factors are im portant and should be considered for every installation :
1. Since sulphur dioxide is heavier than air, it will norm ally tend to settle near the floor or ground, unless it
is heated, m ixed with other gases that are lighter than air, or prevented from settling by air m ovem ent.
2. Consider how rapidly the SO 2 will diffuse into the air. Select a location for the sensor as close as practical
to an anticipated source.
3. Consider ventilation characteristics of the im m ediate area. Air m ovem ent will cause the gas to becom e
m ore concentrated in som e areas than others. Always place the sensors where the m ost concentrated
accum ulation of sulphur dioxide gas is anticipated. Also consider the fact that som e ventilation system s
3
do not operate continuously.
4. Locate the sensor away from potential sources of contam ination (dirt, etc.) if possible.
5. The sensor should be installed with the flame arrestor pointing down (refer to Figure 1) to prevent buildup of contam inants and to ensure the device is weather resistant.
6. The sensor m ust be accessible for testing and calibration.
7. Exposure to excessive heat or vibration can cause prem ature failure of electronic devices 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 detection system is of little value if the SO 2 gas cannot readily come in contact
with the sensor. First priority should be placing the sensor where the highest concentration of gas
is anticipated.
W IRING REQUIREM ENTS
Two wire cable is used for connecting the sensor to a transm itter, controller, or display m odule. The use of
shielded cable is highly recom m ended to protect against interference caused by extraneous electrical
"noise."
The m axim um distance between the sensor and controller is lim ited by the resistance of the connecting wiring,
which is a function of the gauge of the wire being used. See below for the m axim um wiring distance allowed
for a given wire size. If a transm itter is used, refer to the transm itter m anual for specific wiring instructions.
Table 2 - Maximum Wiring Distances
Sensor to Controller/Transmitter
W IRE
SIZE
MAXIMUM SENSOR TO
CONTROLLER DISTANCE
(AW G)
Feet
Meters
18
5700
1750
16
9000
2800
4
SENSOR W IRING
1. Determ ine the best m ounting locations for the sensors.
2. Mount the sensor junction box, allowing room between the junction box and the m ounting surface for the
sensor and calibration cup. The junction box should be electrically connected to earth ground.
3. Rem ove the cover from the junction box.
NOTE:
Do not apply power to the system with the junction box cover removed unless the area has been
declassified.
4. Rem ove the cap from the sensor housing.
5. Rem ove the sensing elem ent assem bly from the packaging. Determ ine proper orientation for the
assem bly, then carefully plug it into the sensor housing.
NOTE:
Handle the sensing element assembly carefully. To avoid possible damage, observe the normally accepted
procedures for handling electrostatic sensitive devices. Refer to 'Electrostatic Sensitive Device Handling
Procedure" in the Appendix for further information.
6. Place the cap back on the sensor housing. Do not over tighten.
7. Attach the sensor to the junction box. The sensor should be tight to ensure an explosion proof housing,
but do not over tighten.
NOTE
Coat sensor threads with an appropriate grease to ease installation, and also lubricate the junction box cover
threads to ensure a water-tight enclosure.
8. Connect the sensor wires to the sensor term inal inside the junction box. Connect the controller wiring to
the controller wiring term inal block. Refer to Figure 2 on the next page. Connect the shield to earth ground
at the controller end only. Under norm al conditions, the other end of the shield should not be connected
at the sensor junction box unless such a connection is required by local wiring codes.
W iring Code :
Red lead
:
Black lead :
Green lead :
'+', positive ve
signal
Chassis (earth) ground
9. Check the sensor wiring to ensure proper connections. Place the cover back on the junction box.
5
Figure 2 - Sensor Wiring
6
START-UP PROCEDURE
1. Secure output loads that are actuated by the system to prevent activation of these devices.
2. Check all wiring for proper connection. Be sure that the sensor has been wired properly.
3. Apply power to the system and allow the sensor to operate for about an hour, then perform the "Startup Procedure" and "Calibration Procedure" as outlined in the transm itter, controller, or display m odule
m anual.
4. Place the system in norm al operation.
CALIBRATION
Since each application is different, the length of tim e between regularly scheduled calibrations can vary from
one installation to the next. However, calibration must be perform ed :
C
when a new system is initially put into service,
C
when the sensing elem ent is replaced, and
C
if a transm itter or controller used with the sensor is replaced.
IMPORTANT:
To ensure adequate protection, the SO 2 detection system must be calibrated on a regularly scheduled basis.
It is recom m ended that the sensor be calibrated one hour after power-up and every 30 days thereafter.
Calibration procedures are dependant on the transm itter, controller, or display m odule being used. For best
results, the sensor m ust be calibrated using sulphur dioxide m ixed with either air or nitrogen and should be
perform ed using 50% of full scale range calibration gas. i.e. ful scale range is 10 PPM calibrate with 5 PPM.
Follow the "Calibration Procedure" outlined in the m anual supplied with the transm itter, controller, or display
m odule used with the sensor.
If background SO 2 is present, it m ay be necessary to purge the sensor with clean air (for the zero reading)
to ensure accurate calibration.
MAINTENANCE
To ensure reliable protection, it is im portant to check and calibrate the SO 2 detection system on a regularly
scheduled basis. The frequency of these checks will vary depending on conditions such as relative hum idity,
dirty or dusty environm ents, and concentration of SO 2.
Relative hum idity is an im portant factor in the life expectancy of a sensor. Constant exposure to extrem ely dry
conditions will shorten the sensor life. If possible sensors, that are operated in extrem ely dry areas should
periodically be rotated to m oister environm ents. A sensor that has been exposed to extrem ely dry
environm ents and can no longer be spanned during calibration or has low sensitivity can be treated. The
sensor should be placed in a m oistened sealed bag and put in the refrigerator for 24 to 48 hours. If this does
not help, the sensor m ust be replaced.
For protection from the environm ent, a rain shield should be used in out-door applications and a dust cover
should be used in dirty or dusty environm ents.
7
SENSING ELEM ENT REPLACEM ENT
The sensing elem ent assem bly is not intended to be repaired. W hen calibration can no longer be perform ed
properly, the assem bly m ust be replaced. Spare sensing elem ent assem blies should be kept on hand for field
replacem ent.
Care should be taken in storing the spare sensing elem ent assem blies. For m axim um protection against
contam ination and deterioration, they should not be rem oved from the original protective packaging until the
tim e of installation. To ensure m axim um storage life, sensing elem ents should be stored at a tem perature
between 0/C and 20/C (32/F and 68/F) and a relative hum idity between 15 and 90 percent.
The area m ust be de-classified or power to the sensor m ust be rem oved prior to replacing the sensing
elem ent in a hazardous area.
To replace the sensing elem ent in the SO2-20-24 detector :
1. Rem ove power from the sensor.
2. Rem ove the cap from the sensor housing. The detector housing does not have to be rem oved from the
junction box.
3. Rem ove and discard the old sensing elem ent assem bly. Check for corrosion or contam ination on the
term inals inside the sensor enclosure; clean if necessary.
4. Determ ine the proper orientation for the new assem bly, then carefully plug it in.
NOTE:
Handle the sensing element assembly carefully. To avoid possible damage, observe the normally accepted
procedures for handling electrostatic sensitive devices. Refer to 'Electrostatic Sensitive Device Handling
Procedure" for further information.
5. Place the cap back on the sensor housing. Tighten only until snug; do not over tighten.
6. Re-apply power.
7. Allow tim e for the sensor to warm -up (approximately one hour for best results), then calibrate. Alw ays
calibrate after replacing the sensing elem ent.
NOTE
The sensing element assembly contains an acid that occasionally can leak. If a leakage should occur, handle
the assembly carefully to prevent any acid from contacting the skin. If acid should come in contact with the
skin, wash the affected area thoroughly with soap and water. Never attempt to open the sensing element
assembly.
8
TROUBLESHOOTING
Table 3 - Troubleshooting Guide
PROBLEM
RECOM M ENDATION
No 4 - 20 mA output.
1. Check the 24Vdc pow er input. Recall +ve goes to red and signal
goes to black.
2. Check that the green LED on the sensor is on. If off, check wiring,
especially the polarity. Also check for proper connection at the
sensor's plug-in connector in the junction box.
Fluctuating current
output.
1. Check that all connections are good.
2. Check for AC noise interference on the cable. If noise does
appear, contact your local distributer for assistance.
Cannot zero on
calibration.
1. If used with a transmitter, controller, or display module, check for
AC noise on the cable. If noise does appear, contact your local
distributer.
Cannot span on
calibration.
1. Check the current output from the sensor. If it is low, the sensor
may have been exposed to an extremely dry environment. Treat
as outlined in the 'M aintenance' section.
Low sensitivity.
1. Sensor may have been exposed to an extrem ely dry environment.
Treat as outlined in the 'M aintenance' section.
2. Check for a dirt deposit on the flam e arrestor. Clean if necessary.
Use a dust cover in dirty or dusty environments, or a rain shield
out-doors.
9
APPENDIX A Electrostatic Sensitive Device Handling Procedure
W ith the trend toward increasingly widespread use of m icroprocessors and a wide variety of other
electrostatic sensitive sem iconductor devices, the need for careful handling of equipm ent containing these
devices deserves m ore attention than it has received in the past.
Electrostatic dam age can occur in several ways. The m ost fam iliar is by physical contact. Touching an object
causes a discharge of electrostatic energy that has built up on the skin. If the charge is of sufficient m agnitude,
a spark will also be visible. This voltage is often m ore than enough to dam age som e electronic com ponents.
Som e devices can be dam aged without any physical contact. Exposure to an electric field can cause dam age
if the electric field exceeds the dielectric breakdown voltage of the capacitive elem ents within the device.
In som e cases, perm anent dam age is instantaneous and an im m ediate m alfunction is realized. Often,
however, the sym ptom s are not im m ediately observed. Perform ance m ay be m arginal or even seem ingly
norm al for an indefinite period of tim e, followed by a sudden and m ysterious failure.
Dam age caused by electrostatic discharge can be virtually elim inated if the equipm ent is handled only in a
static safeguarded work area and if it is transported in a package or container that will render the necessary
protection against static electricity. Net Safety Monitoring Inc. m odules that m ight be dam aged by static
electricity are carefully wrapped in a static protective m aterial before being packaged. Foam packaging blocks
are also treated with an anti-static agent.
If it should ever becom e necessary to return the m odule, it is highly recom m ended that it be carefully
packaged in the original carton and static protective wrapping.
Since a static safeguarded work area is usually im practical in m ost field installations, caution should be
exercised to handle the m odule by its m etal shields, taking care not to touch electronic com ponents or
term inals.
In general, always exercise all of the accepted and proven precautions that are norm ally observed when
handling electrostatic sensitive devices.
A warning label is placed on the packaging, identifying those units that use electrostatic sensitive
sem iconductor devices.
* Published in accordance with EIA standard 471
10
APPENDIX B Wire Resistance In Ohms
DISTANCE
(FEET)
AWG #20
AWG #18
AWG #16
AWG #14
AWG #12
AWG #10
AWG #8
100
1.02
0.64
0.4
0.25
0.16
0.1
0.06
200
2.03
1.28
0.08
0.51
0.32
0.2
0.13
300
3.05
1.92
1.2
0.76
0.48
0.3
0.19
400
4.06
2.55
1.61
1.01
0.64
0.4
0.25
500
5.08
3.2
2.01
1.26
0.79
0.5
0.31
600
6.09
3.83
2.41
1.52
0.95
0.6
0.38
700
7.11
4.47
2.81
1.77
1.11
0.7
0.44
800
8.12
5.11
3.21
2.02
1.27
0.8
0.5
900
9.14
5.75
3.61
2.27
1.43
0.9
0.57
1000
10.20
6.39
4.02
2.53
1.59
1.09
0.63
1250
12.70
7.99
5.03
3.16
1.99
1.25
0.79
1500
15.20
9.58
6.02
3.79
2.38
1.50
0.94
1750
17.80
11.20
7.03
4.42
2.78
1.75
1.10
2000
20.30
12.80
8.03
5.05
3.18
2.00
1.26
2250
22.80
14.40
9.03
5.68
3.57
2.25
1.41
2500
25.40
16.00
10.00
6.31
3.97
2.50
1.57
3000
30.50
19.20
12.00
7.58
4.76
3.00
1.88
3500
35.50
22.40
14.10
8.84
5.56
3.50
2.21
4000
40.60
25.50
16.10
10.00
6.35
4.00
2.51
4500
45.70
28.70
18.10
11.40
7.15
4.50
2.82
5000
50.10
32.00
20.10
12.60
7.94
5.00
3.14
5500
55.80
35.10
22.10
13.91
8.73
5.50
3.46
6000
61.00
38.30
24.10
15.20
9.53
6.00
3.77
6500
66.00
41.50
26.10
16.40
10.30
6.50
4.08
7000
71.10
44.70
28.10
17.70
11.10
7.00
4.40
7500
76.10
47.90
30.10
19.00
12.00
7.49
4.71
8000
81.20
51.10
23.10
20.20
12.70
7.99
5.03
9000
91.40
57.50
36.10
22.70
14.30
8.99
5.65
10 000
102.00
63.90
40.20
25.30
15.90
9.99
6.28
NOTE: RESISTANCE SHOWN IS ONE WAY. THIS FIGURE SHOULD BE DOUBLED WHEN DETERMINING CLOSED LOOP
RESISTANCE.
11
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