Detcon, Inc.
TP-424C Hydrogen Sulfide Sensor
Operator’s Installation & Instruction Manual
March 18, 2014 • Document #2324 • Version 2.2
Table of Contents
3.0 Description
3.1 Principle of Operation
3.2 Constant Temperature Control
3.3 One Man Remote Calibration
3.4 Application and Interference Data
3.5 Specifications
3.6 Installation
3.7 Start Up
3.8 Calibration
3.9 Calibration Frequency
3.10 Heater Voltage Adjustment
3.11 Fault Supervision
3.12 Trouble-shooting
3.13 Parts List
3.14 Warranty
3.15 Service Policy
Detcon Model TP-424C Hydrogen Sulfide Sensor PG.2
3.0 DESCRIPTION
Construction of
Semiconductor Sensor
Sensor
Film
Heater
Film
Silicon
Microchip
Detcon Model TP-424C, hydrogen sulfide sensors are designed to detect and monitor H2S in air over the
range of 0-100 ppm. The sensor assembly consists of a solid state semi-conductor sensor in a stainless steel
ousing, a plug-in control transmitter circuit, a base connector board and an explosion proof enclosure. The
h
sensor assembly is suitable for use in Class I; Div. 1; Groups B, C, D electrically classified areas.
Sensor Technology
The sensor technology is a patented solid state metal oxide semiconductor. The sensor consists of two thin
films; a temperature sensitive heater film, and an hydrogen sulfide sensitive sensor film. Both films are
deposited on a silicon microchip by vacuum deposition. The heater film elevates the operating temperature
of the sensor film to a level where a good sensitivity and response to hydrogen sulfide is achieved. The sensor
film is a proprietary metal oxide that shows a dynamic response to hydrogen sulfide gas. Range of sensitivity
is from part per billion to % by volume. The rugged sensor is capable of maintaining its operating characteristics for periods of up to 7-10 years in most industrial environments and as such, is supported by a 10-year
conditional warranty.
Plug in Control Transmitter Circuit
The control transmitter is a remote mounted electronic circuit designed and packaged as a plug-in module.
The transmitter assembly consists of several circuit functions: input power conditioning, sensor heater control, sensor signal conditioning, sensor fault supervision, and fault LEDs. A metallic face plate with pull
ring identifies test points and calibration adjustments. The plug-in module design supports easy field level
maintenance and repair. The mating plug is gold plated for maximum resistance to corrosion.
Detcon Model TP-424C Hydrogen Sulfide Sensor PG.3
Base Connector Board
T
P-424C
C
OARSE
+
P
PM H2S
4
-
2
0 mADC
T
E
X
A
S
H
O
U
S
T
O
N
TEMP
HEATER
detcon inc.
SPAN
FINE
SIGNAL
CURRENT
VOLT
SIG
FLT
H
TR
FLT
BLUE
YELLOW
MA
24VDC
To Controller
Ter m i n a ls
BLACK
WHITE
Sensor
–
+
4-20MA
The base connector board is mounted in the explosion proof enclosure and includes: the mating connector
for the control transmitter, reverse input and secondary transient suppression, input filter, and lugless terminals for all field wiring.
Explosion Proof Enclosure
The explosion proof enclosure is constructed of cast metal with an epoxy finish. The enclosure is fitted
with a threaded cover. Electrical classification is Class I; Div. 1, Groups B, C, D
Detcon Model TP-424C Hydrogen Sulfide Sensor PG.4
3.1 PRINCIPLE OF OPERATION
P
RE-AMP
(
SPAN)
C
ONSTANT
TEMPERATURE
C
ONTROL
S
IGNAL
CONDITIONING
X
MTR
POWER
S
UPPLY
MOS
S
ENSOR
R
TD
HEATER
I/O CIRCUIT
PROTECTION
S
IGNAL OUT
POWER IN
In operation TP-424C sensors are installed in industrial areas where hydrogen sulfide gas leaks are most likely to occur. Method of detection is by diffusion adsorption. As hydrogen sulfide gas diffuses through the sin-
ered porous filter and contacts the surface of the heated sensor element, the metal oxide sensor film decreas-
t
es in electrical resistance non-linearly proportional to the concentration of gas. This change in resistance is
conditioned by a control transmitter circuit which, in turn, provides a linear 4-20 mA DC signal corresponding to the range 0-100 ppm. As the gas leak subsides and the area clears, the sensor film returns to its original
resistance range. In application, sensor operation is a continuous reading detection/monitoring method.
3.2 CONSTANT TEMPERATURE CONTROL
A unique feature of the TP-424C solid state sensor is the RTD type heater film. The heater film serves two
important functions. First, it elevates the operating temperature of the sensor film to a level where most
efficient response and clearing characteristics are achieved. And second, it allows control circuits to control
surface temperature of the sensor film regardless of ambient temperature conditions. This constant temperature method improves long term stability and overall accuracy, as well as improves sensor performance in
cold weather applications.
3.3 ONE MAN REMOTE CALIBRATION
Sensor assembly design incorporates a modular plug-in remote control transmitter which accommodates
all calibration adjustments: span (coarse and fine) and heater voltage. A metallic face plate protects against
damage and allows easy access to test points and trimming potentiometers. With the use of a digital voltmeter, the design supports one man remote calibration.
3.4 APPLICATION & INTERFERENCE DATA
Model TP-424C sensors are designed to detect and monitor hydrogen sulfide gas in ambient air in the
range of 0-100 parts per million. Minimum sensitivity and scale resolution is 1 ppm. Sensor specifications
reflect an operating temperature range of -40° F. to +175° F. While the sensor is capable of operating outside these temperatures, performance specifications are verified within the limit.
Sensor Placement/Mounting
Sensor location should be reviewed by facility engineering and safety personnel. Area leak sources and
perimeter monitoring are typically used to determine number and location of sensors. Hydrogen sulfide gas
is slightly heavier than air (approximately 1.18); therefore, the sensors are generally located 2 - 4 feet above
grade. The sensors should always be mounted in accessible locations to facilitate periodic maintenance.
Interference Data
Methane 25,000 = 0
Ethane 5,000 = 0
Hexane 5,000 = 0
Propane 5,000 = 0
Butane 5,000 = 0
Carbon Monoxide 800 = 0
Carbon Dioxide 5,000 = 0
Carbon Disulfide 14 = 0
Methanol 500 = 3
Isopropanol 500 = 1
Detcon Model TP-424C Hydrogen Sulfide Sensor PG.5
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