GLH-320 is an electronic module used in Kongsberg’s radar tank gauging / tank monitoring systems (GL-300 / GLA / GLK series).
It is covered under the EU–Type Examination Certificate Sira 14ATEX2056X as part of the GLH-320 module used in GLA-300 / GLA-310 systems
The certificate states that for the GLH-320 module, the ambient temperature limits differ when used in single or dual radar configurations.

Specific entity parameters (electrical limits, capacitances, inductances) are given in the certificate for GLH-320 in relation to its intrinsically safe interfaces.
Also, a Kongsberg certificate document mentions “GLH-320” and “GL-320” in the context of certification for use in explosive atmospheres with details on temperature range etc.
The “M1-NO” suffix likely refers to a specific variant or configuration (for example, a “module 1, no option,” or “no output” or similar) — but I couldn’t find a public source that decodes that exact suffix with certainty.