Overview - GMP251 - GMP252

Relay Box for GMP250 Carbon Dioxide Probes Quick Guide

Document code
English (United States)
Document type
User guide

The GMP250 relay box allows using the analog current (mA) output channel of Vaisala CARBOCAP® Carbon Dioxide Probes GMP251 and GMP252 for relay control.

The voltage (V) output channel is not used for relay control with the relay box: the voltage channel provides CO2 measurement output (feedthrough via the relay box) in the same manner as when wired directly without the relay box.

The relay configuration (activation and release limits, error state output) is done using GMP251/252 serial line interface commands.

Table 1. GMP250 Relay Box Specifications
Property Specification
Maximum switching voltage 50 VDC, 50 VAC
Maximum switching power 30 W, 30 VA
Number of relays 1
Probe output to relay
  • Current output to relay control: ppm CO2
  • Voltage output through the relay box: ppm CO2 or % CO2
Probe power supply requirements 20 ... 30 VDC supplied through the relay box
Relay configuration interface Serial line (Vaisala Industrial Protocol)
Using GMP251/252 for relay control requires using the Vaisala Industrial Protocol serial line interface to configure the probe to use relays, and wiring the probe to send output and receive power through the relay box.
This Quick Guide instructs how to carry out the serial line configuration and wiring related to using the current output for relay control. For more information on GMP251/252 serial line commands and other functionalities, see the user documentation of the probes:
  • GMP251 User Guide (M211799EN)
  • GMP252 User Guide (M211897EN)