Comet T8348, T8448 Instruction Manual

www.cometsystem.cz

Instruction Manual

T8348 programmable indoor transmitter

of temperature and CO2 concentration
with RS232 serial output

T8448 programmable indoor transmitter

of temperature and CO2 concentration

with RS485 serial output

2 IE-SNC-T83(4)48-03

© Copyright: COMET System, Ltd.
It is prohibited to copy and make any changes in this manual, without

explicit agreement of company COMET System, Ltd. All rights reserved.
COMET System, Ltd. makes constant development and improvement of

their products. Manufacturer reserves the right to make technical changes
to the device without previous notice. Misprints reserved.

Manufacturer is not responsible for damages caused by using the device in
conflict with this manual.

To damages caused by using the device in conflict with this manual can not
be provide free repairs during the warranty period.

Read carefully instruction manual before the first device connection.

IE-SNC-T83(4)48-03 3

Table of contents

GENERAL DESCRIPTION ......................................................................... 4

DEVICE SETTING FROM THE MANUFACTURER .................................... 6

DEVICE INSTALLATION ........................................................................... 7

INFO MODE ............................................................................................... 9

DESCRIPTION OF COMMUNICATION PROTOCOLS ............................ 10

MODBUS RTU .........................................................................................10

PROTOCOL COMPATIBLE WITH ADVANTECH-ADAM STANDARD ...12

ARION COMMUNICATION PROTOCOL - AMIT COMPANY .................13

TROUBLESHOOTING ............................................................................. 14

ERROR STATES OF THE DEVICE .........................................................14

TECHNICAL SUPPORT AND SERVICE .................................................14

TECHNICAL DATA .................................................................................. 15

MEASURED VALUES ..............................................................................15

GENERAL SPECIFICATIONS .................................................................15

OPERATING CONDITIONS ....................................................................16

END OF OPERATION .............................................................................16

DIMENSIONS ...........................................................................................17

TYPICAL APPLICATION WIRING ...........................................................17

APPENDIX A ............................................................................................ 18

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General description

The transmitters are designed for online measurement of carbon dioxide
concentration and temperature of air in a building interiors.

device type

construction type

output

galvanic isolated output

T8348

ambient air

RS232

no

T8448

ambient air

RS485

yes

The CO2 concentration is measured using the dual wavelength NDIR
sensor with multiple point adjustment. The dual wavelength NDIR CO2
sensing procedure compensates aging of the sensing element and offers
maintenance free operation and outstanding long term stability. Measured

values can be read in „SLOW mode“ (filtered, averaged) or in „FAST
mode“ (current values without averaging). SLOW mode has advantages in

applications like climate control because of filtering short time peaks. As an
example exhaled air from an employee passing the sensor could affect the
climate control negatively with a short response time because the control
would trigger a change of the ventilation based on this one-time

measurement. On the contrary in „FAST mode“ no software filter is used
for calculating the output value. This fact adds a noise of typ. ±30ppm

which has to be considered in terms of accuracy. The measured value of
CO2 concentration depends on the value of air pressure, (the altitude at the
place of installation). For this reason, it is suitable for accurate
measurement to set the altitude of the installation site by TSensor software

- see below.
Measured values are displayed on dual line LCD display. The visual

indication of CO2 concentration is provided by three-color LED.
After power up of the device starts internal test. During this time (about

20s) LCD display shows (----) instead of CO2 concentration value.
Supported communication protocols are Modbus RTU, protocol compatible

with standard Advantech-ADAM and protocol ARION. Devices are preset
from manufacturer to Modbus RTU communication protocol. If you would
like to use different communication protocol then Modbus RTU, it is
necessary preset them throw user’s software – see below.

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Use software Tsensor for setting of all device parameters (recommended).
It is free to download at www.cometsystem.cz. It supports make the
adjustment of the device too. This procedure is described at file
„Calibration manual.pdf“ which is installed commonly with the software.
Change of some parameters is possible to do without user’s software with
Windows hyperterminal (change of communication protocol, its

parameters, LCD display setting). It is described in file “Description of
communication protocols” ( free to download at www.cometsystem.cz ).

Models marked TxxxxZ are non-standard versions of the transmitters.
Description is not included in this manual.

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Device setting from the manufacturer

If special setting was not required in the order device is set from the
manufacturer to the following parameters:

communication protocol: Modbus RTU
device address: 1
communication speed: 9600Bd, without parity, 2 stop bits
display: switched ON
value displayed at higher line: CO2 concentration
value displayed at lower line: temperature
temperature unit: °C
measurement CO2 mode: “SLOW“
LED indication: up to 1000 ppm lights green LED, between

1000 and 1200 ppm lights yellow LED and
over 1200 ppm lights red LED

altitude: 300 m above see level at the installation site