Dwyer CDTA Series Communicating Carbon Dioxide Detector Instruction Manual
- June 4, 2024
- Dwyer
Table of Contents
CDTA Series Communicating Carbon Dioxide Detector
Instruction Manual
The Series CDTA and CDTC Communicating Carbon Dioxide Detector combine the
function of several room sensors into a single, compact housing. Both the
Series CDTA and the CDTC’s parameters include carbon dioxide, temperature,
and temperature set point with override while the CDTA also includes a
humidity sensor.
By having field selectable Modbus® and BACnet Communications, only four wires
are needed for power and the communication signal. The communicating detectors
can be daisy-chained together to further reduce installation costs. In order
to reduce the setup time, the RS-485 MAC address is set up using onboard DIP
switches. The second set of DIP switches is used to select whether the output
is Modbus® RTU or BACnet MS/TP communication protocols and to limit access to
the setup menu.
The barometric pressure can be programmed to correct for altitude. The
humidity parameter in the Series CDTA uses a capacitive polymer sensor and the
temperature is measured using a 10KΩ thermistor sensor.
Optional local and remote displays are available to display any of the
parameters. For applications in which the building occupants aren’t familiar
with CO2 concentrations, the LCD can be programmed to display temperature,
humidity (only for Series CDTA), or temperature set point instead. For
environments occupied 24 hours per day it is recommended to periodically
expose the CO2 sensor to outside ambient air.
INSTALLATION
WARNING
Disconnect the power supply before installation to prevent electrical shock
and equipment damage. Make sure all connections are in accordance with the job
wiring diagram and in accordance with national and local electrical codes. Use
copper conductors only.
NOTICE
Avoid locations where severe shock or vibration, excessive moisture, or
corrosive fumes are present.
NOTICE
Do not exceed the ratings of this device, permanent damage not covered by
warranty may result.
MOUNTING
- Push the tab on top and bottom of the cover and lift the cover from the back plate (See Figure 1).
- Select the mounting location, away from diffusers, lights, or any external influences.
- Mount the transmitter on a vertical surface to a standard electrical box using the two #6 M2C type screws provided.
- Pull wires through the sub-base hole and make necessary connections.
- Reattach the cover to the base plate.
SPECIFICATIONS
Sensor: CO2: NDIR 15-year life expectancy; Humidity: Capacitive
polymer; Temperature: 10KΩ thermistor.
Range: CO2: 0 to 2000 or 5000 PPM
CO2 (depending on model); Humidity: 0
to 100% RH; Temperature: 32 to 122 °F (0 to 50 °C).
Accuracy*: CO2: ±40 PPM ±3% of reading 2000 PPM; ±50 PPM + 5% of reading
5000 PPM; RH: ±2% (10 to 90% RH); Temperature: ±1°C @ 25°C.
Response Time (CO2): 2 min for 99% step change.| Temperature Limits: 32 to
122°F (0 to 50°C).
Humidity Limits: 0 to 85% (non-condensing).
Power Requirements: 10-42 VDC/10-30 VAC.
Power Consumption: Average: 0.5
watts; Peak: 1.2 watts.
Device Load: 1/8 unit load.
Output: 2-wire RS-485, Modbus® RTU or BACnet MS/TP communication protocol.
Weight: 4.4 oz (125 g).
Agency Approvals: BTL, CE.
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WIRING
NOTICE
Wiring should comply with Electrical Characteristics of Generators and
Receivers for Use in Balanced Digital Multipoint Systems, TIA/EIA-485-A-1998,
Telecommunications Industry Association, 1998.
NOTICE
Use electrostatic discharge precautions (e.g., use of wrist straps) during
installation and wiring to prevent equipment damage.
When using a common power supply, wire the CDTA and CDTC as shown in Figure 2,
using two twisted pair conductors. One pair is to be used for B[+] and A[-].
The other pair is to be used for power and common. This configuration is not
suitable for AC supplies. Use a DC supply only. Care should be taken that
there are not too many devices powered from the same supply as voltage drops
will occur in the wiring. If you have many devices or have long cable runs,
the local supply configuration may be a better choice.
When using a dedicated local power supply, wire the CDTA and CDTC as shown in
Figure 3, using a twisted pair and a single conductor. The pair is to be used
for B[+] and A[-]. The single conductor is to be used for common. Both AC and
DC supplies are suitable for this configuration.
In either configuration, the B[+] and A[-] lines must be terminated at both
ends with a 120 Ω resistor. If the CDTA is an end device it has an on-board
resistor that may be used. See DIP SWITCH SETTINGS to enable it.
SETUP AND DIP SWITCH CONFIGURATION
Use DIP Switch SW2 to configure the RS-485 MAC address of the device. The
address assignment is determined by adding the values for each of the switches
that are in the ON position Table 1 below.
| Switch Position | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 |
|---|---|---|---|---|---|---|---|---|
| Address Value | 128 | 64 | 32 | 16 | 8 | 4 | 2 | 1 |
Table 1: Address value for each switch position
The CDTA and CDTC come from the factory with all of the DIP switches, except
position 1, in the ON position as shown in Figure 4 below. The address of the
transmitter would be 127 as it would be 64+32+16+8+4+2+1 = 127. Another
example would be if the address desired was 008, the only DIP switch position
in the ON position would be position 5.
A valid address depends on the protocol selected. Valid BACnet addresses range
from 0 to 127. Valid Modbus® addresses range from 1 to 247. A valid and unused
address should be set before connecting to an existing network. The device
will not function properly if an invalid address is set. During the power-up
sequence, the LCD (if present) will display the RS-485 address as the primary
value with “ADR” as the primary text and either “BAC” to indicate BACnet or
“MOD” to indicate Modbus® as the secondary text. If the RS-485 MAC address is
invalid, the invalid value is shown as the primary value with “ERR” as the
primary text.
Use DIP Switch SW1 (see Figure 5) to configure other hardware and software options per Table 2 below.
Switch
1 – Menu Enable
2 – Protocol
3 – Reserved
4 – Terminating Resistor| On
Access to the setup menu is enabled
Modbus®
120Ω between A[-] and B[+]| Off
Access to the setup menu
is disabled BACnet Open
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Table 2: DIP switch menu options
AUTO SERIAL CONFIGURATION
Auto serial configuration enables the device to determine the baud rate,
parity, and stop bits directly from the serial traffic. This allows a device
to be quickly and easily deployed after a valid RS-485 MAC address is chosen.
Note that the auto-configuration procedure assumes a serial configuration
appropriate to the selected protocol as follows:
SUPPORTED SERIAL CONFIGURATIONS
Protocol
| Supported Baud Rates| Data Size| Parity|
Stop Bits
BACnet| 9600
19200
38400
57600
76800
115200
| 8| None| 1
Modbus® – RTU| Even
Odd| 1
None| 2
Table 3: Supported serial configurations
If this is not the case, then the serial communication must be configured
manually in the setup menu.
To activate the auto serial configuration, set a valid RS-485 MAC address
using DIP switch SW2, connect the serial bus and power wires, and apply power.
The device will power up and begin examining the serial bus for communication.
When Modbus® is selected, and the device is set up offline or away from the
main network, it is necessary to generate traffic in order to configure the
serial communication.
Attempting to read input registers is a good method to generate traffic. Note
that while the serial configuration is in progress, the device may not respond
to requests. The device may require multiple read requests to complete the
serial configuration process.
The auto serial configuration process will complete once a message addressed
to the device is received and processed successfully. The serial configuration
parameters are then saved to non-volatile storage and loaded by default each
time the device starts. If the serial configuration of the bus changes, a
power cycle of the device is required to restart the Auto Serial
Configuration process.
USER INTERFACE
Home Screen
For models with the LDC display option, or when using the A-449A remote
display tool, the home (idle) screen displays up to two measured values and is
the steady state of the device. The information displayed on the home screen
can be changed by the “DSP” value in the setup menu.
Set Point
When idle, a single press of either the UP or DOWN button will display the
current set point value with the selected units displayed as the primary text.
Additional presses of the UP or DOWN buttons will increase or decrease the set
point value by 1 degree.
A press and hold of the UP or DOWN button will initiate continuous changing of
the set point value. The set point display will timeout and return to the home
screen after 5 seconds of inactivity. At this point, the new set point value
is stored in non-volatile memory. The range of the set point value can be
configured with “SOH” and “SOL” values in the setup menu. A display is not
required to change the set point value.
Override
When on the home screen or when changing the set point, the override button
(middle button) can be pressed. When the override button is pressed in these
states, a snowflake symbol is displayed momentarily to indicate the button was
pressed.
Setup Menu
The setup menu provides a means to configure the device locally. The setup
menu can only be entered if the Menu Enable switch is in the on position and a
display is present (local or remote). To enter the setup menu, press and hold
the UP and DOWN buttons for at least 3 seconds or until the display changes.
The setup menu contains a scrollable list of values that can be changed. Use
the UP and DOWN buttons to scroll through the available values. The scrollable
list is circular to allow continuous scrolling in either direction.
A value can be modified by first scrolling to the desired value, then pressing
and holding the UP and DOWN buttons for at least 0.5 seconds, or until to word
SET is displayed. The value can now be changed with the UP and DOWN buttons.
Numerical values are displayed in the primary value area of the display with
the current units in the primary text area. Some settings are text-based and
only show values in the primary text area.
When the desired value is reached, press and hold the UP and DOWN buttons for
0.5 seconds to store the value in non-volatile memory and return to the setup
menu.
The setup menu will timeout and return to the home screen after 30 seconds of
inactivity. The setup menu can also be exited manually by a press and hold of
the DOWN button for 0.5 seconds.
SETUP MENU VALUES
V alue| Description| V alue|
Description
DSP| Home screen configuration
Units selection
Set point low limit temperature Set point high limit temperature Typical
barometric pressure Relative humidity offset| OFT| Temperature offset
UNI| OFC| CO2 offset
SOL| AUT| Auto serial configuration
SOH| BAU| Baud rate selection
BAR| PAR| Parity selection
OFH| STP| Stop bits selection
| RST| Reset to factory defaults
Only the Series CDTA has humidity sensing capabilities.
Table 4: Setup values
Home Screen Configuration (DSP)
This value controls what information is displayed on the home screen.
DSP
Setting
V alue
| Primary
V alue
| Primary
T ext
| Secondary
V alue
| Secondary
T ext
“CH”| CO2 concentration| “PPM”| Relative humidity| “%”
“CT”| CO2 concentration| “PPM”| Temperature| “°C” or “°F”
“HT”| Relative humidity| “%”| Temperature| “°C” or “°F”
“TS”| Temperature| “°C” or “°F”| Setpoint| “°C” or “°F”
“S”| Setpoint| “°C” or “°F”| |
“T”| Temperature| “°C” or “°F”| |
“H”| Relative humidity| “%”| |
“C”| CO2 concentration| “PPM”| |
Only the Series CDTA has humidity sensing capabilities.
Table 5: Display values
Units Selection (UNI)
This value controls the units that data is displayed.
SOL
Default Value| Minimum Value| Maximum Value| Increment
20°C (68°F)| 0°C (32°F)| Set point high limit| 1°
T able 7: Set point for low-temperature limit Set Point High Limit
Temperature (SOH)
This value sets an upper limit on the current set point value. The set
point high limit value is a numerical setting that supports continuous change
(increment/decrement) by pressing and holding of either the UP or DOWN button.
If the new set point high limit temperature is lower than the current set
point temperature, then the set point temperature will be set to the new set
point high limit temperature.
SOH
Default Value
| Minimum Value| Maximum Value|
Increment
35°C (95°F)| Set point low limit| 50°C (122°F)| 1°
T able 8: Set point for high-temperature limit A verage
Atmospheric Carbon Dioxide Value (AAC)
This parameter sets the value at which the sensor’s automatic background
calibration will reference. The factory setting is derived from research from
the National Oceanic and Atmospheric Administration (NOAA).
AAC
Default Value| Minimum Value| Maximum Value| Increment
Derived from NOAA| 200 PPM| 9999 PPM| 1 PPM
T able 9: Average atmospheric carbon dioxide value
T ypical Barometric Pressure (BAR)
This value sets the typical barometric pressure for the location where the
device is mounted. The factory setting is for standard pressure at sea level.
Adjusting the barometric pressure gives a more accurate measurement,
especially at higher elevations.
BAR
Default Value
| Minimum Value| Maximum Value|
Increment
1013 hPa| 677 hPa| 1016 hPa| 1 hPa
(29.9 inHg)| (20.0 inHg)| (30.0 inHg)| (0.1 inHg)
T able 10: Elevation/barometric pressure compensation Relative
Humidity Offset (OFH)
This value, allows the relative humidity to be adjusted by a fixed amount
to match another calibrated measurement. The display shows the current
relative humidity value plus any previous offset value.
RHU
Default Value| Minimum Value| Maximum Value|
Increment
0%| -30%| 30%| 0.1%
T able 11: RH offset value T emperature Offset (OFT)
This value allows the temperature to be adjusted by a fixed amount to match
another calibrated measurement. The display shows the current temperature
value plus any previous offset value.
OFT
Default Value| Minimum Value| Maximum Value| Increment
0°| -30°| 30°| 0.1°
Holding Registers
The holding registers allow the device to be completely configured remotely
after being connected the Modbus® network.
The Override State register indicates if the override button has been pressed.
The override button only sets the Override State register to 1. The Override
State register must be written with a value of 0 to return it to the non-
asserted state.
The Reboot Device register allows a Modbus® master to remotely request this
device to perform a warm reset. When a value of 1 is written to this register,
the device will respond with success. The reset will take place approximately
5 seconds after the command was received. Writing a value of 0 to this
register has no effect.
HOLDING REGISTERS
Register| Description| Data Type| V alue| Range
0001
0002
0003
0004
0005
0006
0007*
0008
0009
0010
0500
| Override State
Set Point Temperature in 1°C or °F
Set Point High Limit Temperature in 1°C or °F
Set Point Low Limit Temperature in 1°C or °F
CO2 Offset in PPM
Typical Barometric
Pressure in 1hPa or
0.1inHg
Relative Humidity Offset in 0.1%
Temperature Offset in
0.1°C or °F
Display Mode
System of units selection Reboot device
| Unsigned 16bit integer Unsigned 16bit integer Unsigned 16bit integer
Unsigned 16bit
integer
Signed 16bit integer Unsigned 16bit integer
Signed 16bit integer Signed 16it integer
Unsigned 16bit integer Unsigned 16bit integer Unsigned 16bit integer
| 0 – 1
0 – 50
(32 – 122)
0 – 50
(32 – 122)
0 – 50
(32 – 122)
±500
677 – 1016
(200 – 300)
±300
±300
0 – 7
0 – 1
0 – 1
| 0 or 1
0 – 50°C
(32 – 122°F)
0 – 50°C
(32 – 122°F)
0 – 50°C
(32 – 122°F)
±500
677 – 1016hPa
(20.0 – 30.0 inch)
±30.0%
±30.0°C/°F
See Table 3
0 – US Customary
1 – SI
0 – Do nothing
1 – Warm Reset
*Only the Series CDTA has humidity sensing capabilities.
MAINTENANCE/REPAIR
Upon final installation of the Series CDTA and CDTC, no routine maintenance is
required. The Series CDTA and CDTC are not fielded serviceable and should be
returned if repair is needed. Field repair should not be attempted and may
void the warranty.
This symbol indicates waste electrical products should not be disposed of with
household waste. Please recycle where facilities exist. Check with your Local
Authority or retailer for recycling advice.
WARRANTY/RETURN
Refer to “Terms and Conditions of Sale” in our catalog and on our website.
Contact customer service to receive a Return Materials Authorization number
(RMA) before shipping the product back for repair. Be sure to include a brief
description of the problem plus any additional application notes.
DWYER INSTRUMENTS, INC.
Phone: 219-879-8000
Fax: 219-872-9057
www.dwyer-inst.com
e-mail: info@dwyermail.com
P.O. BOX 373 • MICHIGAN CITY, INDIANA 46360, U.S.A.
References
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