The Vaisala HMT370EX provides humidity, temperature and moisture measurement in hazardous areas containing potentially explosive gases or dust, with certified configurations for operation up to Zone 0 and Zone 20.
The Vaisala HUMICAP® HMT370EX Series is designed for humidity, temperature and moisture measurement in hazardous and potentially explosive environments. Certified configurations allow the complete transmitter to be installed directly in areas classified up to Zone 0 for gases and Zone 20 for combustible dust.
The series is suitable for chemical and pharmaceutical production, paint booths, fuel storage, powder processes, food manufacturing, hydrogen systems, oil and gas applications and other processes where ordinary electrical measurement equipment cannot be installed safely.
Six standard humidity-and-temperature probe styles cover wall mounting, confined spaces, high pressure, high temperature, high humidity and pressurised pipelines. Dedicated HMP378F and HMP378H versions measure moisture in oil and JET A-1 fuel.
| Probe | Designed For | Key Capability |
|---|---|---|
| HMP371 | Wall mounting and ambient hazardous-area measurement | Fixed 12 mm probe; −40 to +60 °C |
| HMP373 | Confined spaces, ducts and channels | Compact 12 mm remote probe; up to +120 °C with FEP cable |
| HMP374 | Pressurised spaces and vacuum chambers | 0–10 MPa pressure range; −70 to +180 °C |
| HMP375 | High-temperature processes | Long 13.5 mm probe; −70 to +180 °C |
| HMP377 | Continuous high humidity and near-condensing processes | High-humidity construction; −70 to +180 °C; up to 1 MPa |
| HMP378 | Pressurised pipelines | Adjustable insertion depth; 0–4 MPa; ball-valve installation option |
| HMP378F | Moisture in industrial oil | Water activity, relative saturation, temperature and calculated ppm in supported oils |
| HMP378H | Moisture in JET A-1 fuel | Water activity, relative saturation and temperature in aviation fuel |
HMT370EX is available with regional certifications including ATEX, IECEx, CML, NEPSI, KCs, FM, CSA and UKEX. The exact approval and marking depend on the ordered configuration and destination country.
| Certification Region | Highest Published Classification |
|---|---|
| Europe — ATEX | II 1 G Ex ia IIC T4 Ga; II 1 D Ex ia IIIC T200 85 °C Da |
| International — IECEx | Ex ia IIC T4 Ga; Ex ia IIIC T200 85 °C Da |
| United Kingdom — UKEX | II 1 G Ex ia IIC T4 Ga; II 1 D Ex ia IIIC T200 85 °C Da |
| United States — FM | Class I Zone 0 and Zone 20; Class I, II and III Division 1 classifications according to certificate |
| Canada — FM/CSA | Intrinsically safe Zone and Division classifications according to the selected approval |
| Japan, China and Korea | CML, NEPSI and KCs certified configurations are available |
| Measurement Specification | Performance |
|---|---|
| Relative-Humidity Range | 0–100% RH at a maximum dew-point temperature of +95 °C |
| RH Accuracy at +23 °C | ±0.8% RH from 0–90% RH |
| RH Factory-Calibration Uncertainty | ±0.5% RH from 0–40% RH; ±0.8% RH from 40–95% RH |
| RH Response Time | 15 seconds, T63 |
| Humidity Sensor | Vaisala HUMICAP R2 |
| Maximum Temperature Range | −70 to +180 °C, depending on probe and Ex temperature class |
| Temperature Accuracy at +23 °C | ±0.1 °C |
| Temperature Sensor | Pt1000 RTD Class F0.1 according to IEC 60751 |
Available calculated parameters depend on the selected probe and configuration.
| Feature | Specification |
|---|---|
| Operating Voltage | 12–28 V through an approved intrinsic-safety interface |
| Analog Outputs | Two two-wire 4–20 mA channels |
| Analog-Output Accuracy | Typically ±0.0625% of full scale at +20 °C |
| Electrical Connection | Screw terminals for 0.33–2.0 mm² or AWG 14–22 conductors |
| Transmitter Service Connection | Vaisala service cable 219690 |
| Probe Service Connection | Vaisala USB2 adapter |
| Environmental Specification | Operating Limit |
|---|---|
| Electronics Temperature | −40 to +60 °C |
| Display-Model Temperature | −20 to +60 °C |
| Storage Temperature | −40 to +70 °C |
| Probe-Head Humidity | Up to +100 °C dew-point temperature |
| Protection with Probe Connected | IP66 |
| Protection with Probe Detached | IP54 |
| Housing Material | EN AW-6082 aluminium alloy |
| Housing Weight | Approximately 1.5 kg, depending on display configuration |
The maximum permissible probe temperature depends on the probe type, cable material, gas or dust classification and required temperature class. A probe capable of measuring +180 °C cannot automatically be used at +180 °C under every Ex classification.
| Example Temperature Class | Typical Published Probe-Head Limit |
|---|---|
| T6 | Up to approximately +55 °C for applicable remote-probe configurations |
| T5 | Up to approximately +100 °C for applicable remote-probe configurations |
| T4 | Up to approximately +135 °C for HMP374/HMP375/HMP377/HMP378 variants |
| T3 | Up to +180 °C for applicable HMP374/HMP375/HMP377/HMP378 variants |
Always use the temperature limits in the certificate and safety guide supplied for the exact ordered model.
The HMP371 fixed probe attaches directly to the probe body and is suitable for ambient humidity and temperature measurement in hazardous rooms and enclosures. It measures from −40 to +60 °C and can also be ordered as a temperature-only configuration.
The compact 12 mm HMP373 is suitable for ducts, channels and restricted installation spaces. Rubber-cable versions operate up to +80 °C, while FEP-cable versions support probe-head temperatures up to +120 °C, subject to Ex temperature-class limitations.
The HMP374 is designed for pressurised vessels, compressed gas spaces and vacuum chambers. It supports process pressures from vacuum to 10 MPa and temperatures from −70 to +180 °C, depending on the hazardous-area classification.
The long HMP375 separates the probe body from the hottest part of the process and is intended for heated industrial processes. Its measurement range extends from −70 to +180 °C with a compatible temperature class and installation.
The HMP377 is designed for persistent high humidity and near-condensing environments. It supports probe heating strategies and external temperature compensation where accurate relative humidity is required during heating.
The HMP378 provides adjustable insertion depth for installation in pressurised pipelines. It supports pressures up to 4 MPa and can be installed through a compatible ball valve for easier insertion and removal within the permitted installation pressure.
| Probe | Measured Medium | Available Parameters |
|---|---|---|
| HMP378F | Industrial oils | Water activity, relative saturation, temperature and calculated water content in supported oils |
| HMP378H | JET A-1 aviation fuel | Water activity, relative saturation and temperature |
The HMT370EX is powered and read through approved intrinsic-safety interfaces installed according to the selected Ex certificate. The barriers limit the electrical energy that can enter the hazardous area.
| Interface Option | Purpose |
|---|---|
| Zener Barrier | Energy-limiting interface that requires the specified high-integrity earth arrangement |
| Galvanic Isolator | Provides intrinsic-safety isolation between hazardous-area and safe-area circuits |
| One Barrier per Channel | Each active 4–20 mA channel requires the appropriate certified interface arrangement |
Vaisala offers one- and two-channel barrier or isolator accessories. Final selection must be verified against the transmitter entity parameters, cable capacitance and inductance, receiving equipment and local installation standards.
HMT370EX measurement signals can be incorporated into the Vaisala viewLinc Continuous Monitoring System through a properly engineered analog-input and intrinsic-safety interface.
The Vaisala CAB100 Industrial Cabinet can be configured with analog inputs and safety barriers for suitable hazardous-area monitoring projects. This provides an organised safe-area interface between field transmitters and the viewLinc monitoring network.
| System Stage | Function |
|---|---|
| HMT370EX in Hazardous Area | Measures humidity, temperature, oil moisture or fuel moisture according to probe configuration |
| Certified Safety Barrier | Limits electrical energy crossing into the hazardous area |
| CAB100 Safe-Area Cabinet | Centralises compatible barriers, power components, analog inputs and communication equipment |
| viewLinc Server | Provides records, alarms, reporting, audit trails and user-access control |
The detachable probe module allows the probe to be removed for calibration outside the hazardous area without removing the complete transmitter body. Replacement-probe settings can be restored from the transmitter with minimal reconfiguration.
Calibration, adjustment and configuration can be performed through the optional local display or using Vaisala Insight PC software and the correct service accessory in a safe location. The transmitter is also compatible with the Vaisala Indigo80 handheld indicator using the specified connection cable.
Seacom Process Instruments supplies and supports the Vaisala HMT370EX intrinsically safe humidity and temperature transmitter in Malaysia for hazardous chemical, pharmaceutical, paint, food, oil, gas, fuel and industrial applications.
Our team can assist with probe selection, certification, measurement range, installation accessory, intrinsic-safety barrier, CAB100 cabinet integration, viewLinc monitoring architecture, commissioning and calibration planning.
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The Vaisala HMT370EX provides humidity, temperature and moisture measurement in hazardous areas containing potentially explosive gases or dust, with certified configurations for operation up to Zone 0 and Zone 20.
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HMT370EX Series Catalogue
- Intrinsically Safe Humidity and Temperature Transmitter Series HMT370EX
(1.11M)
