Detcon TP-624C - Manual (Page 5)

3.1 P RINCIPLE OF O PERATION
Method of detection is by diffusion/adsorption. Air and gas diffuse through a sintered stainless steel filter and contact
the heated surface of the metal oxide sensor film. As hydrogen sulfide gas molecules react with oxygen ions on the
film, there is a decrease in electrical resistance proportional to the gas concentration. The heater film elevates the tem-
perature of the sensor film creating convection and promoting a quick response to changing gas concentrations.
Electronically, the heater film is used to maintain a constant temperature of the sensor film enhancing stability and
repeatability. The sensor response is reversible and results in continuous monitoring of ambient air conditions.
3.2 A
PPLICATION
Model TP-624C MicroSafe™ sensors are designed to detect and monitor hydrogen sulfide gas in ambient air in the
range of 0-100 parts per million. The sensor can also be programmed to operate in the range 0-20 ppm or 0-50 ppm.
Minimum sensitivity and scale resolution is 1 ppm. Operating temperature range is --40° F. to +175° F. While the sen-
sor is capable of operating outside these temperatures, performance specifications are verified within the limit.
3.2.1 Sensor Placement/Mounting
Sensor location should be reviewed by facility engineering and safety personnel. Area leak sources and perimeter
mounting are typically used to determine number and location of sensors. Hydrogen sulf ide gas is slightly heavier
than air (approximately 1.18); therefore, the sensors are generally located 2 - 4 feet above grade.
3.2.2 Interference Data
Gas PPM
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 Disulf ide 14 = 0
Methanol 200 = 0
Isopropanol 200 = 0
Ammonia 500 = 0
Diesel Fuel = 0
Demethyl Sulf ide 4.4 = 0
Ethylene 200 = 0
Freon 12 1000 = 0
Hydrogen 1000 = 8
Methyl Mercaptan 5 = 8
Sulfur Dioxide 300 = 0
Toluene 32 = 0
Ethanol 200 = 0
Detcon Model TP-624C Hydrogen Sulfide Sensor PG.5
Functional
Block
Diagram
Functional
Block
Diagram
Analog 4-20 mA Out
Power In
Relays Out
Pre-Amp Display
Temperature
Compensation
Alarm & Fault
Relays
RS-485 & 4-20mA
Micro-
processor
Transmitter
Power Supply
Sensor
Element
I/O Circuit
Protection
Serial RS-485 Out