Series-HHT

Supported Applications

The Series HHT Hazardous Area Humidity/Temperature Transmitter is built to take accurate measurements in the harshest of environments. It is offered in explosion-proof and intrinsically-safe versions so the same measurement platform can be specified for classified areas such as chemical processing, oil and gas facilities, spray and paint operations, and other locations where flammable gases, vapors, or dusts may be present.

The explosion-proof models provide a humidity output, while the intrinsically-safe models are available for humidity only or for combined humidity and temperature; the intrinsically-safe versions require an intrinsically-safe barrier to meet their hazardous-area approvals. An aluminum enclosure rated NEMA 4X (IP66) lets the transmitter be mounted outdoors or in wash-down and corrosive settings, and a 1/2 female NPT conduit connection with a screw terminal block simplifies field wiring.

Operating Conditions & Performance

The transmitter measures relative humidity over 0 to 100% RH and temperature over -40 to 140°F (-40 to 60°C). Relative humidity accuracy is ±2% across 10 to 90% RH, and temperature accuracy is ±0.9°F at 77°F (±0.5°C at 25°C). Hysteresis is ±1%, repeatability is ±0.1% typical, and drift is specified at less than 1% RH per year. Resolution is 0.1% RH for humidity and 0.1°F (0.1°C) for temperature, with a response time of 15 s.

The unit is rated for storage over -40 to 176°F (-40 to 80°C). The output is a 4 to 20 mA signal, provided as two channels on humidity/temperature models with loop power on the RH channel. Power requirements depend on the protection method: intrinsically-safe HHT-IX models operate on 9.5 to 28 VDC, and explosion-proof HHT-EX models operate on 16.5 to 28 VDC.

The Series HHT is FM approved and CE marked. It is not field serviceable and should be returned if repair is needed. Use electrostatic-discharge precautions during installation and wiring, and avoid locations subject to severe shock or vibration, excessive moisture, or corrosive fumes.

Configuration Options

Models differ in three ways: the type of hazardous-area protection, the parameters measured, and whether an LCD is fitted.

• Protection: explosion-proof models are designed to contain an internal ignition, while intrinsically-safe models limit energy in the circuit and require an intrinsically-safe barrier. This distinction also sets the supply-voltage window — 16.5 to 28 VDC for explosion-proof units versus 9.5 to 28 VDC for intrinsically-safe units.
• Measured parameters: explosion-proof models output humidity only, whereas the intrinsically-safe range includes both humidity-only and combined humidity/temperature versions. Combined models provide two 4 to 20 mA channels.
• Display: LCD versions add a local display of the measured value; non-LCD versions transmit only.

Key Product Differences

The Series HHT model chart comprises:

• HHT-EU — explosion-proof, humidity, no display.
• HHT-IU — intrinsically safe, humidity, no display.
• HHT-IT — intrinsically safe, humidity/temperature, no display.
• HHT-EU-LCD — explosion-proof, humidity, with display.
• HHT-IT-LCD — intrinsically safe, humidity/temperature, with display.

Available accessories include the A-287 mounting bracket for pipe or surface mounting and the A-450 replacement sintered filter.