Vaisala GMP251 User manual

2091 Exchange Court
Fairborn, Ohio 45324
937-426-2703
www.NexSens.com
Vaisala GMP 251/252 CO2 Probe
Quick Start Guide
1
The Vaisala GMP251 and GMP252 Carbon Dioxide probes are compatible with the
Nexsens X2 data logger using RS485 Modbus RTU output.
Note that the GMP25x sensor membrane and cable connection are NOT
waterproof. A waterproof, gas-permeable membrane must be installed on the
sensor and the green M12 cable connection must be waterproofed prior to
deployment.
Wiring
Note: Most sensors will have factory-installed UW connectors. If this is the case,
skip to the Configuring the Vaisala GMP 251/252 section.
For compatibility, a Vaisala sensor cable must be fitted with a NexSens UW
connector to interface with the X2 data logger.
For user-wiring with a NexSens UW-Field Wireable Plug (UW-FWP) follow the wiring
diagram below.
Vaisala 223263SP Cable
Wire Color
Sensor
Signal
UW-FWP J Pin
Connection
Brown
12 to 30 VDC Power
J5
Blue
Power GND
J2
White
RS485-B
J7
Black
RS485-A
J8
Configuring the Vaisala GMP 251/252
Note: All GMP25x sensors not integrated by NexSens technology require the use of
a PC terminal connection and Vaisala’s USB interface cable to modify the sensor
output.
1. Download or launch a terminal emulation software. NexSens recommends
Tera Term as a free open-source option.
2. Connect the Vaisala USB cable and verify Windows properly downloads the
necessary drivers automatically. Verify this appears as a unique COM port
connection in Window’s Device Manager.

2091 Exchange Court
Fairborn, Ohio 45324
937-426-2703
www.NexSens.com
Vaisala GMP 251/252 CO2 Probe
Quick Start Guide
2
3. Navigate to Select|Serial Port. Choose the appropriate COM port for the
Vaisala cable and establish a terminal connection using the default GMP
settings shown.
Baud Rate: 19200 Baud
Data: 8 Data Bits
Parity: none
Stop: 1 Bit
4. While connecting the GMP25x sensor to the Vaisala USB cable,
simultaneously press and hold the [Enter] key.
Once successful an output of the model and sensor version will appear
in the terminal.
5. The following commands must be sent to configure the sensor for an X2-
connection.
Smode: Set to MODBUS to set communication as Modbus RTU.
Address: Configure the sensor address to 1if it is the only Modbus
RTU sensor. Each sensor must have a unique address to communicate.
COM1: Set the COM 1 settings similar to the image below.
If used with a NexSens data logger, follow the quick start guide included
with the logger for a complete setup of the sensor.