Using HMT370EX Series transmitters in hazardous locations - HMT370EX

HMT370EX User Guide

Document code
English (United States)
Document type
User guide
WARNING Protected installation using galvanic isolators or Zener barriers is mandatory in a hazardous environment.

In hazardous environments, always connect the transmitters via galvanic isolators or Zener barriers. A galvanic isolator or Zener barrier must also be used when the transmitter and probe body are in a safe area, but the probe head is installed in a hazardous environment. For wiring information, see the galvanic isolator and Zener barrier wiring diagrams included in this document.

HMT370EX does not include a galvanic isolator or a Zener barrier. They can be ordered as optional accessories from Vaisala.
WARNING HMT370EX series transmitters have been designed for use in hazardous locations as specified by the product classification. The personnel installing, using, or maintaining HMT370EX transmitters are responsible for determining the appropriate protection concept for the specific application HMT370EX is used in, and that the hazardous area classification of the device meets the requirements of the application.
WARNING If the equipment is used in a manner not specified by Vaisala, the protection provided by the equipment may be impaired.

HMT370EX series transmitters are certified for use in hazardous areas as defined by the following classifications:

Table 1. HMT370EX series hazardous area classifications
Certification HMT370EX classification
IECEx 1 / ATEX 2

II 1 G Ex ia IIC T4 Ga

II 1 D Ex ia IIIC T200 85 °C Da

-40 °C ≤ Tamb ≤ +60 °C

CAUTION The personnel installing, operating, and maintaining HMT370EX transmitters must have the required competencies for working in the hazardous location, as defined by the applicable standards.

For information on the standards that apply to using HMT370EX based on the classification of the device, see HMT370EX certification documentation and the declarations of conformity related to HMT370EX at

1 International certification
2 EU certification