Vaisala HMD82M, HMW88M Technical Note

M212167EN-A

Technical Note

Adjustment of Relative Humidity and
Temperature

HMD82M and HMW88M Transmitters

Overview

This document provides instructions for adjustment of relative humidity and temperature in Vaisala
HMD82M and HMW88M humidity and temperature transmitters.

For the adjustment procedure, you will need the following:

• USB service cable (order code ASM212800)

• Computer with:

• Windows operating system

• Free USB port

• Driver for the USB service cable installed. See Taking USB Service Cable into Use

(page 2).

• Terminal application (for example PuTTy). See Connecting to HMD82M/HMW88M

(page 2).

• Medium-size crosshead screwdriver (Pozidriv) for the screws on the cover

• Small slotted screwdriver for the screw terminals

Using Service Port

The HMD82M and HMW88M transmitters have a serial interface on the component board for user
adjustment. You can connect to it through the 4-pin M8 service port connector on the transmitter.
Vaisala
your PC.

oers an optional USB service cable (order code ASM212800) for connecting the transmitter to

The service port is intended for short-term use such as adjustment. For permanent installation, use the
analog output.

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Vaisala Oyj
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FI-01670 Vantaa, Finland
Phone:[phone]
© Vaisala 2018

All rights reserved. Any logos and/or product names are trademarks of Vaisala or its individual partners.
Any reproduction, transfer, distribution or storage of information contained in this document is strictly
prohibited. All specifications — technical included — are subject to change without notice.

Technical Note M212167EN-A

If you have not used the HMD82M/HMW88M USB service cable before, install first the driver for the
cable. See Taking USB Service Cable into Use (page 2).

Taking USB Service Cable into Use

Before taking the USB service cable into use, you must install the USB driver on your PC. The following
instructions are for PCs with Windowsâ operating system.

1. Check that the USB service cable is not connected. Disconnect the cable if you have already
connected it.

2. Download the driver from http://www.ftdichip.com/Drivers/VCP.htm.

3. Execute the USB driver installation program (setup.exe), and accept the installation defaults. The
installation of the driver may take several minutes.

4. After the driver has been installed, connect the USB service cable to a USB port on your PC.
Windows will detect the new device, and use the driver automatically.

5. The installation has reserved a COM port for the USB service cable. Remember to use the correct
port in the settings of your terminal program.
To check the reserved COM port number:

a. Open Control Panel from the Windowsâ Start menu. Search for "devices and printers" in

the Control Panel application.
b. Locate the USB cable 'TTL232R-3V3' in the list of devices.
c. Right-click to select Properties, then select Hardware. The COM port number is given in

brackets in the Properties dialog of the cable.

Connecting to HMD82M/HMW88M

The following steps describe how to connect to the HMD82M/HMW88M transmitter using a USB
service cable and PuTTY terminal application for Windows (available for download at

www.vaisala.com/en/search/download).

For the default serial interface settings, see Table 1 (page 3).

Connecting the USB service cable to the transmitter may distort the readings from the
analog outputs on the module component board due to ground loop.

1. Connect the USB cable between your PC and the service port of the transmitter.

2. Start the PuTTY application.

3. Select the Serial & USB settings category, and check that the correct COM port is selected in the
Serial or USB line to connect to

4. Check that the other serial settings are correct for your connection, and change if necessary.
Flow control should be set to None unless you have a reason to change it.

5. Select Open to open the connection window and start using the serial line.

If PuTTY is unable to open the serial port you selected, it will show you an error message instead.
If this happens, restart PuTTY and check the settings.

field.

HUM and T

2 (8)

Technical Note M212167EN-A

6. You may need to adjust the Local echo setting in the Terminal category to see what you are
typing on the serial line. To access the configuration screen while a session is running, click the
right mouse button over the session window, and select Change Settings... from the pop-up
menu.

Figure 1 PuTTY Terminal Application

Table 1 HMD82M and HMW88M Default Serial Interface Settings

Property Description / Value

Baud rate 19200

Parity None

Data bits 8

Stop bits 1

Flow control None

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