Instruction Manual

ManualsBrandsVaisala ManualsToolsGMD20

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.

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.

min 80 max 140

Ø15

Summary of content (4 pages)

PAGE 1
CO2 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.
PAGE 2
CO2 transmitter GMD20 and GMD20D M210292en-A The nominal 24 V supply must be connected between terminals + and -. The analogue output is available at remaining terminals. The common wire is connected to terminal 0 and the other wire either to terminal V (voltage output) or to terminal mA (current output). The current output type is chosen with the jumper 0/4mA (see Figure 2): 4...20mA is chosen by connecting the jumper (default) and the 0...20 mA is chosen by disconnecting the jumper.
PAGE 3
CO2 transmitter GMD20 and GMD20D M210292en-A POWER SUPPLY REQUIREMENTS The GMD20 transmitter is designed to operate from a nominal 24 VAC/VDC supply. The power supply should maintain the voltage between 18...30 VDC or 20...26 VAC for all load conditions and all mains voltages. The power input includes a halfwave rectifier. To avoid current peaks, it is recommended to use a DC supply. The average transmitter current consumption is 85 mA maximum but peak currents of 170 mA may occur during normal operation.
PAGE 4
CO2 transmitter GMD20 and GMD20D M210292en-A TECHNICAL DATA Carbon dioxide Measuring range 0...2000 ppm CO2 (nominal); with recalibration 0...5000 ppm CO2 , 0...10 000 ppm CO2 , 0...20 000 ppm CO2 Accuracy at 20°C against certified factory references <±[30 ppm + 2.0 % of the reading] (including repeatability and calibration uncertainty) Non-linearity <±1.0 %FS Temperature dependence of output (typical) < 0.