Vaisala GMD20 User Manual

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transmitter GMD20 and GMD20D

M210292en-A

INTRODUCTION

Vaisala's GMD20 uses silicon based CARBOCAP

sensor technology providing

excellent stability and reliability. The GMD20 transmitters require almost no

maintenance: the recommended calibration interval is five years in HVAC and related

benign applications. Transmitters are available without a display (GMD20 version) and

with a display (GMD20D version).

MOUNTING

The GMD20 transmitters are truly duct mounted. The distance between the probe and the

duct wall is easily adjusted by using the mounting plate. The mounting plate is fastened

with four screws ST.4.2x16-C-Z/A4m DIN 7981. Note that four

3.2 holes on the duct

surface are needed, as well as one

22...25 mm hole in the middle (see figure below).

Insert the transmitter through the mounting plate and adjust the distance.

min 80 max 140

Ø15

Figure 1 Dimensions of the GMD20 and the mounting plate (in mm)

ELECTRICAL CONNECTIONS

Open the transmitter cover and remove the display board if there is one installed. The

cable is inserted through a rubber plug included in the package. Pierce the rubber plug

with a screwdriver or a similar instrument in order to open the hole for the cable. Then

insert the plug in the appropriate hole in the transmitter cover. Strip a few millimetres of

the cable insulation and insert the cable carefully through the rubber plug so that you can

connect the wires to the terminal block on the righthand side of the component board.

Page 1: Electrical Connections
(GMD20D version). MOUNTING The GMD20 transmitters are truly duct mounted. The distance between the probe and the duct wall is easily adjusted by using the mounting plate. The mounting plate is fastened with four screws ST.4.2x16-C-Z/A4m DIN 7981. Note that four 3.2 holes on the duct...
Page 2 The default relay trigger point has been set to 1000 ppm and it can be changed with the optional software kit 19222GM. For further details, contact your local Vaisala representative. If an optional LonWorks interface or a relay output option is installed in the GMD20, please, refer to the corresponding manuals for details.
Page 3 CONNECTION TO A 24 VAC SUPPLY The GMD20 transmitters can also be connected to a 24 VAC supply without an external rectifier. However, when more than one transmitter is connected to one 24 VAC transformer, a common loop is formed and there is an increased risk of a short-circuit. To avoid this, always use separate floating supply for each transmitter (see Figure 3A).
Page 4: Technical Data
Calibration software kit (incl. disk and serial COM adapter) GUARANTEE Vaisala issues a guarantee for the material and workmanship of this product under normal operating conditions for one (1) year from the date of delivery. Exceptional operating conditions, damage due to careless handling and misapplication will void...

Gmd20d