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Stevens / Dyacon - Model GT-1 / GT-2 -Globe Temperature Sensor
The Globe Temperature (GT) sensor measures the temperature of the environment in a way that mimics how humans and animals perceive heat. GT absorbs heat from radiation such as the sun, air, and convection.
A GT sensor with the WBGT calculation helps indicate how hot it feels to a human body by considering air temperature, humidity, and direct sunlight or other radiation sources for an assessment of heat stress levels.
While Heat Index is commonly used by the general public, WBGT is a better indicator for heat stress in the sun. Heat index is calculated from temperature in the shade and relative humidity. WBGT also uses the temperature and humidity in its calculation, but temperatures are measured in direct sunshine using the GT. According, the GT sensor is used in conjunction with other sensors to calculate the “Wet Bulb Globe Temperature” (WBGT) heat stress index.
OSHA and many others also use the WBGT as a guide to managing workload in direct sunlight, as do athletic departments (college and high school) and events. Application that benefits from predicting heat stress:
- Sports / athletes
- Workplace safety
- military personnel
- Extreme heat forecast
- Outdoor recreation
- Livestock management
- Crop growth
- Climate change research
The Globe Temperature sensor consists of black-coated, hollow cooper sphere (the globe) that absorbs heat from various sources including radiation. The black coating helps to absorb heat effectively. This sphere is designed for harsh outdoor conditions.
Inside the GT-1 is a digital temperature sensor for Modbus communication protocol and the GT-2 incorporates an analog thermistor sensor.
Globe Temperature Sensor GT-1TM is a high-quality temperature sensor designed for permanent and semipermanent installations. The instrument is used to take measurements in environments of worker heat stress.
GT-1 uses a low-power digital-output module with a Modbus interface. It is compatible with Modbus host devices, such as programmable logic controllers (PLCs) and data loggers.
User-accessible registers for sensor calibration allow the instrument to be calibrated using Modbus messages.
Globe Temperature Sensor GT-2TM is a high-quality temperature sensor designed for permanent and semipermanent installations. The instrument is used to take measurements in environments of worker heat stress.
GT-2 uses a thermistor probe internally, specifically Dyacon Stainless Steel Thermistor Probe TSSP-1TM.
The NTC thermistor element is double encased and capable of long-term outdoor exposure in harsh freeze-thaw environments.
The globe aggregates radiant energy sources, ambient air temperature, and air movement that can be used to approximate a human body exposure.
Combined with humidity and ambient air temperature , globe temperature can be used to calucate wet-bulb globe temperature (WBGT).
This heat stress measurement are used to monitor environments for worker comfort, athletic events, miltary shoulder engagement, live stock, and over all stress and safety in outdoor activities with direct sun exposure.
Temerature Measurement
- Range: -40°C to 80°C
- Resolution: 0.05°C
- Accuracy: (0°C to 60°C) +/- 0.2 K*
- Reproducibility: +/- 0.1 K
- Time Constant: 5.6 min
- Long Term Drift: <0.05 K/yr
- Sensor Type: PTAT
Electrical
- Power: Input 5 VDC to 24 VDC
- Current: 1.4 mAavg at 12 VDC full run mode† 60 uAavg in sleep mode‡
Mechanical
- Material: Copper globe with polyester coating. Aluminum and bronze fittings
- Overall (WxDxH): 15 cm x 15 cm x 25.9 cm (6” x 6” x 10.2”)
- Cable: 4 conductor, 24 AWG, stranded Foil shield w/ drain wire Outdoor rated cable
- Total Weight: 0.78 kg (1.76 lb)
Data
- Protocols: Modbus RTU slave , RS485, half-duplex User configurable baud rate, parity, and stop bits. 19200, N, 8,1 default
Environmental
- Operating Temperature: -40°C to 60°C
- Storage Temperature: -40°C to 80°C
- Water: Direct rain and snow exposure
Thermistor Specifications
- Resistance: 10k ohms @ 25°C
- Interchangeability Tolerance: +/- 0.1°C (within 0°C to 70°C / 32°F to 158°F)
- Measurement Range: -40°C to 105°C (-40°F to 220°F)
- Storage Temperature: -40°C to 105°C (-40°F to 220°F)
- Dissipation Constant: 2 mW/°C
- Time Constant: 8 s, still air
Mechanical Features
- Globe Material: Copper globe with polyester coating. Delrin machined mounting hardware.
- Overall (WxDxH): 15 cm x 15 cm x 25.9 cm (6” x 6” x 10.2”)
- Cable to Thermistor Connection: Thermistor leads welded to cable
- Cable Length: 6 m (20 ft)
- Wire: 22 AWG, 7 x 30, tin plated, PVC
- Cable Jacket: PVC, gray
- Cable Diameter: 3.8 mm (0.15”)
- Mount: 33 mm (1.3”) diameter pipe
- Total Weight: 0.78 kg (1.76 lb)
- Internal Probe Material: Stainless steel