Dwyer CDTA, CDTC User guide

PWR COM B[+] A[-]

Bulletin AQ-CDTA-CDTC-2

TO

SUPPLY

NEXT

PWR COM B[+] A[-]

1.10

[76.20]

[1

[71.12]

®

Series CDTA and CDTC Communicating Carbon Dioxide Detector

Specications - Installation and Operating Instructions

North American Style

The Series CDTA and CDTC Communicating Carbon Dioxide Detector combines
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 eld 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 cost. In order to reduce the set up

time, the RS-485 MAC address is set up using on-board DIP switches. A second set
of DIP switches are used to select whether output is Modbus® RTU or BACnet MS/TP

communication protocols and to limit access to the set up 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

national and local electrical codes. Use copper conductors only.

Avoid locations where severe shock or vibration, excessive

NOTICE

NOTICE

MOUNTING

1. Push tab on top and bottom of cover and lift cover from back plate (See Figure 1).

2. Select the mounting location, away from diffusers, lights or any external inuences.

3. Mount transmitter on a vertical surface to a standard electrical box using the two #6
M2C type screws provided.

4. Pull wires through sub base hole and make necessary connections.

5. Reattach cover to base plate.

Disconnect 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

moisture or corrosive fumes are present.

Do not exceed ratings of this device, permanent damage not
covered by warranty may result.

[27.96]

4.50

14.30]

2.80

SPECIFICATIONS

Sensor: CO
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.

*Only the Series CDTA has humidity sensing capabilities.

**The specied CO2 accuracy is only guaranteed after three weeks of continuous

operation in environments which are intermittently occupied.

WIRING

Wiring should comply with Electrical Characteristics of Generators

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 conguration 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 conguration may be a

better choice.

TO PREVIOUS

2: NDIR 15 year life

NOTICE

NOTICE

DEVICE

PWR
COM

B[+]

A[-]

and Receivers for Use in Balanced Digital Multipoint Systems, TIA/

EIA-485-A-1998, Telecommunications Industry Association, 1998.

Use electrostatic discharge precautions (e.g., use of wrist straps)
during installation and wiring to prevent equipment damage.

1 2 3 4

.552

[14.02]

2x .176

[4.47]

.573

[14.56]

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.

3.000

TO NEXT

DEVICE

PWR
COM

B[+]

A[-]

Figure 2: Common power supply wiring

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 conguration.

In either conguration, 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.

PREVIOUS

Figure 1: Removal of cover from back plate

DWYER INSTRUMENTS, INC.

P.O. BOX 373 • MICHIGAN CITY, INDIANA 46360, U.S.A.

DEVICE

COM

B[+]
A[-]

Figure 3: Local power supply wiring

Phone: [phone]

Fax: [phone]

1 2 3 4

POWER

www.dwyer-inst.com

e-mail: [e-mail]

TO

DEVICE

COM

B[+]

A[-]

SETUP AND DIP SWITCH CONFIGURATION

ENABLE

PROTOCOL RESERVED

TERMINATION

OVERRIDE BUTTON

SECONDARY

Use DIP Switch SW2 to congure 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 comes 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.

ON

1 2 3 4 5 6 7 8

Figure 4: DIP switch SW2 (center-left)

Use DIP Switch SW1 (see Figure 5) to congure other hardware and software options

per Table 2 below.

Switch On Off

1 – Menu Enable

2 – Protocol
3 – Reserved
4 – Terminating Resister

Access to the setup menu
is enabled

®

Modbus

120Ω between A[-] and B[+]

Access to the setup menu
is disabled
BACnet

Open

Table 2: DIP switch menu options

AUTO SERIAL CONFIGURATION

Auto serial conguration enables the device to determine the baud rate, parity and
stop bits directly from the serial trafc. This allows a device to be quickly and easily
deployed after a valid RS-485 MAC address is chosen. Note that the auto conguration
procedure assumes a serial conguration appropriate to the selected protocol as

follows:

SUPPORTED SERIAL CONFIGURATIONS
Protocol Supported Baud Rates Data Size Parity Stop Bits

BACnet 9600

®

Modbus

– RTU Even

19200
38400

57600
76800

115200

8 None 1

Odd
None 2

1

Table 3: Supported serial congurations

If this is not the case, then the serial communication must be congured manually in

the setup menu.

To activate auto serial conguration, 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
network, it is necessary to generate trafc in order to congure the serial communication.
Attempting to read input registers is a good method to generate trafc. Note that while
serial conguration is in progress, the device may not respond to requests. The device
may require multiple read requests to complete the serial conguration process.

The auto serial conguration process will complete once a message addressed to the
device is received and processed successfully. The serial conguration parameters

are then saved to non-volatile storage and loaded by default each time the device

starts. If the serial conguration of the bus changes, a power cycle of the device is
required to restart the Auto Serial Conguration process.

is selected, and the device is setup ofine or away from the main

USER INTERFACE

PRESSED INDICATOR

VALUE

SECONDARY TEXT

PRIMARY TEXT

DIP switch

SW2

ON

1 2 3 4

MENU

NETWORK

Figure 5: DIP switch SW1 (bottom-center)

DIP switch

SW1

PRIMARY VALUE

Figure 7: Display layout

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 congured 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 snow

ake symbol is displayed momentarily to indicate the button was pressed.

Remote display port

Up

Override

Down

Figure 6: Internal view of transmitter

Figure 8: Side view of transmitter

Setup Menu

The setup menu provides a means to congure 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 modied by rst scrolling to the desired value, then press and hold 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
Value Description Value Description

DSP

Home screen conguration

UNI

Units selection

SOL

Set point low limit temperature

SOH

Set point high limit temperature

BAR

Typical barometric pressure

OFH*

Relative humidity offset

OFT

Temperature offset

OFC

CO
AUT
BAU
PAR
STP
RST

2 offset

Auto serial conguration

Baud rate selection

Parity selection

Stop bits selection

Reset to factory defaults

*Only the Series CDTA has humidity sensing capabilities.

Table 4: Setup values

Home Screen Conguration (DSP)

This value controls what information is displayed on the home screen.

DSP
Setting

Value

“CH”*
“CT”
“HT”*
“TS”
“S”
“T”
“H”*
“C”

Primary

Value

CO

2 concentration

CO2 concentration
Relative humidity
Temperature
Set point
Temperature
Relative humidity
CO2 concentration

Primary
Text

“PPM”
“PPM”

“%”
“°C” or “°F”
“°C” or “°F”
“°C” or “°F”
“%”

“PPM”

Secondary

Value

Relative humidity
Temperature
Temperature
Set point

Secondary
Text

“%”
“°C” or “°F”
“°C” or “°F”
“°C” or “°F”

*Only the Series CDTA has humidity sensing capabilities.

Table 5: Display values

Units Selection (UNI)

This value controls the units that data is displayed in.

UNI
Setting Value Description

“US”
“SI”

US customary units (°F, in Hg)
International system units (°C, hPa)

Table 6: Unit values

Set Point Low Limit Temperature (SOL)

This value sets a lower limit on the current set point value. The set point low limit

value is a numerical setting that supports continuous change (increment/decrement)

by press and holding of either UP or DOWN button. If the new set point low limit
temperature is higher than the current set point temperature, then the set point
temperature will be set to the new set point low limit temperature.

SOL
Default Value Minimum Value Maximum Value Increment

20°C (68°F) 0°C (32°F) Set point high limit 1°

Table 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 press and holding of either 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°

Table 8: Set point for high temperature limit

Average Atmospheric Carbon Dioxide Value (AAC)

This parameter sets the value at which the sensors 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

Table 9: Average atmospheric carbon dioxide value

Typical 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
(29.9 inHg)

677 hPa

(20.0 inHg)

1016 hPa

(30.0 inHg)

1 hPa
(0.1 inHg)

Table 10: Elevation/barometric pressure compensation

Relative Humidity Offset (OFH)

This value, allows the relative humidity to be adjusted by a xed 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%

Table 11: RH offset value

Temperature Offset (OFT)

This value allows the temperature to be adjusted by a xed 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°

Table 12: Temperature offset value

CO2 Offset (OFC)

This value allows the CO2 Concentration to be adjusted by a xed amount to match
another calibrated measurement. The display shows the current CO2 concentration
value plus any previous offset value.

OFC
Default Value Minimum Value Maximum Value Increment

0 PPM -500 PPM 500 PPM 1 PPM

Table 13: CO

Auto Serial Conguration (AUT)

This value enables or disables the automatic baud rate detection. If the device fails to

communicate or the serial conguration is not one of the options in Table 3, then this
value should be set to “OFF”. The serial can then be congured manually.

2 offset value

AUT
Setting Value Description

“ON”
“OFF”

Auto baud enabled
Auto baud disabled

Table 14: Automatic baud rate value

Parity Selection (PAR)

This value provides the selection of the desired serial parity. This value is only visible
when the value of AUT is “OFF”.

PAR
Setting Value Description

“NON”
“EVE”
“ODD”

Baud Rate (BAU)

This value provides the selection of the desired serial baud rate. This value is only
visible when the value of AUT is “OFF”.

No parity
Even parity
Odd parity

Table 15: Serial parity value

BAU
Setting Value Baud Rate Setting Value Baud Rate

9.6 K

19.2 K

38.4 K

9,600

19,200
38,400

57.6 K

76.8 K

115.2 K

57,600
76,800

115,200

Table 16: Serial baud rate value

Stop Bits Selection (STP)

This value provides the selection of the desired serial stop bits. This value is only
visible when he value of AUT is “OFF”

STP
Setting Value Description

1
2

One stop bit
Two stop bits

Table 17: Serial stop bits value

Reset To Factory Defaults (RST)

This value, when set to “YES”, will reset all user settings to their default values and
reset the device. This applies to all settings including BACnet writable settings.

BACNET

BACnet installations should comply with ANSI/ASHRAE Standard

NOTICE

Refrigerating and Air-Conditioning Engineers, Inc., 2010

Communications wiring must be in a daisy-chain fashion. Star

NOTICE

BACnet Object Overview

The device supports the following objects:

135-2010 BACnet A Data Communication Protocol for Building
Automation and Control Networks, American Society of Heating,

connections and T connections are not permitted

SUPPORTED BACNET OBJECTS
Object

Type

Device
Analog Input
Analog Input
Analog Input
Binary Value
Binary Value
Analog Value
Analog Value
Analog Value
Analog Value
Analog Value
Analog Value
Analog Value
Analog Value
Analog Value
Analog Value
Analog Value

Dynamically
Creatable

No
No
No
No
No
No
No
No
No
No
No
No
No
No
No
No
No

Dynamically
Deletable

No
No
No
No
No
No
No
No
No
No
No
No
No
No
No
No
No

Object
Identier

607xxx

AI1
AI2
AI3
BV1
BV2
AV1
AV2
AV3
AV4
AV5

AV6

AV7
AV8
AV9
AV10
AV11

Object

Name

CDTA IAQ
CO

2 concentration

Relative humidity*
Temperature
Override
Use SI units
Set point
Set point low limit
Set point high limit
Dew point
Wet bulb

Specic enthalpy

Display mode
CO2 Offset
Barometric pressure
Relative humidity offset*
Temperature offset

*Only the Series CDTA has humidity sensing capabilities.

The default object identier is 607xxx, where xxx is replaced by the MS/TP MAC
address set by DIP switch SW2. The object identier value will change as the MS/TP
MAC address changes. However, if a specic object identier is written via BACnet,
then that value is stored and changes to the MS/TP MAC address will no longer affect
the object identier. Similarly, the default object name includes 607xxx. The object
name will reect the current object identier. If a specic object name is written via
BACnet, then that value is stored and changes to the object identier will no longer

affect the object name.

APDU Timeout values are rounded to the nearest second (1000ms). Values less than
500 will be rounded to 0 and Number of APDU Retries will be set to 0.

BACnet Objects

Device Object

Property Default Value Property Data Type Access

Object Identier

Object Name
Object Type
System Status
Vendor Name

Vendor Identier
Model Name

Firmware Revision
Application Software Version
Location
Description
Protocol Version
Protocol Revision
Protocol Services Supported
Protocol Object Types Supported
Object List
Active COV Subscriptions

Maximum APDU Length Supported

Segmentation Supported
APDU Timeout
Number of APDU Retries

Max Master
Max Info Frames

Device Address Binding
Database Revision
Serial Number (1000)

607xxx
“CDTA IAQ 607xxx”

DEVICE(8)
Operational(0)
“Dwyer Instruments, Inc.”

607

“CDTA-???0-???”
“?.?”
“?.?”

“All-in-One CO2/RH/Temp/SetPoint”

1
12
See PICS
See Table 2
See Table 2

480

NO_SEGMENTATION (3)
6000

3
127
1
Empty
1

BACnetObjectIdentier

CharacterString(32)
BACnetObjectType
BACnetDeviceStatus
CharacterString
Unsigned
CharacterString
CharacterString
CharacterString
CharacterString(32)
CharacterString(32)
Unsigned
Unsigned
BACnetServicesSupported
BACnetObjectTypesSupported
BACnetArray
List of BACnetCOVSubscription
Unsigned
BACnetSegmentation
Unsigned
Unsigned
Unsigned
Unsigned
BACnetAddressBinding
Unsigned
CharacterString

Read/Write
Read/Write

Read
Read
Read
Read
Read
Read
Read

Read/Write
Read/Write

Read
Read
Read
Read
Read
Read
Read
Read

Read/Write
Read/Write
Read/Write
Read/Write

Read
Read
Read

Analog Input – CO2 Concentration

This object represents the current CO2 concentration reading in parts per million. This
object supports COV subscriptions to allow easy monitoring of changing values.

Property Default Value Property Data Type Access

Object Identier

Object Name
Object Type
Present Value
Status Flags
Event State
Reliability
Out Of Service
Units
COV Increment

COV Increment Value:

Default Value Minimum Value Maximum Value Increment

50 PPM 1 PPM 1000000 1 PPM

Analog Input – Relative Humidity, CDTA only

This object represents the current relative humidity reading in percent. This object
supports COV subscriptions to allow easy monitoring of changing values.

Property Default Value Property Data Type Access

Object Identier

Object Name
Object Type
Present Value
Status Flags
Event State
Reliability
Out Of Service

Units
COV Increment

COV Increment Value:

Default Value Minimum Value Maximum Value Increment

2% 0.1% 99.9% 0.1%

Analog Input – Temperature

This object represents the current temperature reading in degrees Celsius or
Fahrenheit depending on the value of the Units property. This object supports COV
subscriptions to allow easy monitoring of changing values. Note that the Units property
is writable. Changing the Units value in this object will change the Units used by the
entire device.

Property Default Value Property Data Type Access

Object Identier

Object Name
Object Type
Present Value
Status Flags
Event State
Reliability
Out Of Service
Units

COV Increment

COV Increment Value:

Default Value Minimum Value Maximum Value Increment

2°C (3.6°F) 0.5°C (0.3°F) 49.9°C (89.9°F) 0.1°C/°F

AI1
“CO2 Concentration”
ANALOG_INPUT (0)
Current reading
0

NORMAL (0)

NO_FAULT_DETECTED(0)
FALSE (0)

Parts-per-million (96)

50

AI2
“Relative Humidity”
ANALOG_INPUT (0)
Current reading
0

NORMAL (0)

NO_FAULT_DETECTED(0)
FALSE (0)

Percent-relative-humidity (29)
2

AI3
“Temperature”
ANALOG_INPUT (0)
Current reading
0

NORMAL (0)

NO_FAULT_DETECTED(0)
FALSE (0)

Degrees-Celsius (62)
or Degrees-Fahrenheit (64)
2 (3.6)

BACnetObjectIdentier

CharacterString
BACnetObjectType
Real
BACnetStatusFlags
BACnetEventState
BACnetReliability
Boolean
BACnetEngineeringUnits
Real

BACnetObjectIdentier

CharacterString
BACnetObjectType
Real
BACnetStatusFlags
BACnetEventState
BACnetReliability
Boolean

BACnetEngineeringUnits
Real

BACnetObjectIdentier

CharacterString
BACnetObjectType
Real
BACnetStatusFlags
BACnetEventState
BACnetReliability
Boolean
BACnetEngineeringUnits

Real

Read
Read
Read
Read
Read
Read
Read

Read/Write

Read

Read/Write

Read
Read
Read
Read
Read
Read
Read

Read/

Write
Read

Read/

Write

Read
Read
Read
Read
Read
Read
Read

Read/Write
Read/Write

Read/Write

Analog Value – Set Point Low Limit

This object represents the minimum allowed set point temperature in degrees Celsius
or Fahrenheit depending on the value of the Units property. Note that the Units
property is writable. Changing the Units value in this object will change the Units used
by the entire device.

Property Default Value Property Data Type Access

Object Identier

Object Name
Object Type
Present Value
Status Flags
Event State
Reliability
Out Of Service
Units

Present Value: If a new value written to this property is higher than the set point present
value, then the set point present value will be set to the new value.

Default Value Minimum Value Maximum Value Increment

20°C (68°F) 0°C (32°F) Set Point High Limit 1°

Analog Value – Set Point High Limit

This object represents the maximum allowed set point temperature in degrees Celsius
or Fahrenheit depending on the value of the Units property. Note that the Units
property is writable. Changing the Units value in this object will change the Units used
by the entire device.

Property Default Value Property Data Type Access

Object Identier

Object Name
Object Type
Present Value
Status Flags
Event State
Reliability
Out Of Service
Units

Present Value: If a new value written to this property is lower than the set point present
value, then the set point present value will be set to the new.

Default Value Minimum Value Maximum Value Increment

35°C (95°F) Set Point Low Limit 50°C (122°F) 1°

Analog Value – Dew Point

This object represents the current calculated dew point temperature in degrees
Celsius or Fahrenheit depending on the value of the Units property. Note that the Units
property is writable. Changing the Units value in this object will change the Units used
by the entire device.

Property Default Value Property Data Type Access

Object Identier

Object Name
Object Type
Present Value
Status Flags
Event State
Reliability
Out Of Service
Units

AV2
“Set Point Low Limit”
ANALOG_VALUE (2)

20(68)

0

NORMAL (0)

NO_FAULT_DETECTED(0)
FALSE (0)

Degrees-Celsius (62) or
Degrees-Fahrenheit (64)

AV3
“Set Point High Limit”
ANALOG_VALUE (2)
35(95)
0

NORMAL (0)

NO_FAULT_DETECTED(0)
FALSE (0)

Degrees-Celsius (62) or
Degrees-Fahrenheit (64)

AV4
“Dew Point”
ANALOG_VALUE (2)
Current reading
0

NORMAL (0)

NO_FAULT_DETECTED(0)
FALSE (0)

Degrees-Celsius (62) or
Degrees-Fahrenheit (64)

BACnetObjectIdentier

CharacterString
BACnetObjectType
Real
BACnetStatusFlags
BACnetEventState
BACnetReliability
Boolean
BACnetEngineeringUnits

BACnetObjectIdentier

CharacterString
BACnetObjectType
Real
BACnetStatusFlags
BACnetEventState
BACnetReliability
Boolean
BACnetEngineeringUnits

BACnetObjectIdentier

CharacterString
BACnetObjectType
Real
BACnetStatusFlags
BACnetEventState
BACnetReliability
Boolean
BACnetEngineeringUnits

Read
Read
Read

Read/Write

Read
Read
Read

Read/Write
Read/Write

Read
Read
Read

Read/Write

Read
Read
Read

Read/Write
Read/Write

Read
Read
Read
Read
Read
Read
Read

Read/Write
Read/Write

Analog Value – Set Point

This object represents the desired set point temperature in degrees Celsius or
Fahrenheit depending on the value of the Units property. Note that the Units property
is writable. Changing the Units value in this object will change the Units used by the
entire device.

Property Default Value Property Data Type Access

Object Identier

Object Name
Object Type
Present Value
Status Flags
Event State
Reliability
Out Of Service
Units

Present Value: The set point value is normally set by the local user with the buttons,
but the set point can be written directly from BACnet.

Default Value Minimum Value Maximum Value Increment

22°C (72°F) Set point low limit Set point high limit 1°C/°F

AV1
“Set Point”
ANALOG_VALUE (2)
22(72)
0

NORMAL (0)

NO_FAULT_DETECTED(0)
FALSE (0)

Degrees-Celsius (62) or
Degrees-Fahrenheit (64)

BACnetObjectIdentier

CharacterString
BACnetObjectType
Real
BACnetStatusFlags
BACnetEventState
BACnetReliability
Boolean
BACnetEngineeringUnits

Read
Read
Read

Read/Write

Read
Read
Read

Read/Write
Read/Write

Analog Value – Wet Bulb

This object represents the current calculated wet bulb temperature in degrees Celsius
or Fahrenheit depending on the value of the Units property. Note that the Units
property is writable. Changing the Units value in this object will change the Units used
by the entire device.

Property Default Value Property Data Type Access

Object Identier

Object Name
Object Type
Present Value
Status Flags
Event State
Reliability
Out Of Service
Units

AV5
“Wet Bulb”
ANALOG_VALUE (2)
Current reading
0

NORMAL (0)

NO_FAULT_DETECTED(0)
FALSE (0)

Degrees-Celsius (62) or
Degrees-Fahrenheit (64)

BACnetObjectIdentier

CharacterString
BACnetObjectType
Real
BACnetStatusFlags
BACnetEventState
BACnetReliability
Boolean
BACnetEngineeringUnits

Read
Read
Read
Read
Read
Read
Read

Read/Write
Read/Write

Analog Value – Specic Enthalpy

This object represents the current calculated specic Enthalpy in kilojoules per

kilogram or BTUs per pound dry air depending on the value of the Units property. Note
that the Units property is writable. Changing the Units value in this object will change
the Units used by the entire device.

Property Default Value Property Data Type Access

Object Identier

Object Name
Object Type
Present Value
Status Flags
Event State
Reliability
Out Of Service
Units

Analog Value – Display Mode

This object represents the current display conguration. Changing this value changes

the information displayed to the user.

AV6
“Specic Enthalpy”

ANALOG_VALUE (2)
Current reading
0

NORMAL (0)

NO_FAULT_DETECTED(0)
FALSE (0)
Kilojoules-per-kilogram
dry-air (149) or BTUs-per­pound dry-air (24)

BACnetObjectIdentier

CharacterString
BACnetObjectType
Real
BACnetStatusFlags
BACnetEventState
BACnetReliability
Boolean
BACnetEngineeringUnits

Read
Read
Read
Read
Read
Read
Read

Read/Write
Read/Write

Property Default Value Property Data Type Access

Object Identier

Object Name
Object Type
Present Value
Status Flags
Event State
Reliability
Out Of Service
Units

Present Value: The value written to this property should be a whole number. The value

maps to the Home Screen Conguration (DSP) value as follows:

Present

Value

7*

6

5*
4
3
2
1*
0

AV7

“Display Mode”

ANALOG_VALUE (2)
7
0

NORMAL (0)

NO_FAULT_DETECTED(0)
FALSE (0)
No-units (95)

DSP

Value Primary Value

“CH”
“CT”
“HT”
“TS”
“S”
“T”
“H”
“C”

2 Concentration

CO
CO2 Concentration
Relative Humidity
Temperature
Set Point
Temperature
Relative Humidity
CO2 Concentration

BACnetObjectIdentier

CharacterString
BACnetObjectType
Real
BACnetStatusFlags
BACnetEventState
BACnetReliability
Boolean
BACnetEngineeringUnits

Primary
Text

“PPM”
“PPM”

“%”
“°C” or “°F”
“°C” or “°F”
“°C” or “°F”
“%”

“PPM”

Secondary

Value

Relative Humidity
Temperature
Temperature
Set Point

Read
Read
Read

Read/Write

Read
Read
Read

Read/Write

Read

Secondary
Text

“%”
“°C” or “°F”
“°C” or “°F”
“°C” or “°F”

*Only the Series CDTA has humidity sensing capabilities.

Analog Value – Relative Humidity Offset, CDTA only

This object represents the Relative Humidity Offset value (OFH).

Property Default Value Property Data Type Access

Object Identier

Object Name
Object Type
Present Value
Status Flags
Event State
Reliability
Out Of Service
Units

Present Value: This value allows the relative humidity to be adjusted by a xed amount

to match another calibrated measurement.

AV10
“Relative Humidity Offset”
ANALOG_VALUE (2)
0
0

NORMAL (0)

NO_FAULT_DETECTED(0)
FALSE (0)
Percent-relative-humidity
(29)

BACnetObjectIdentier

CharacterString
BACnetObjectType
Real
BACnetStatusFlags
BACnetEventState
BACnetReliability
Boolean
BACnetEngineeringUnits

Read
Read
Read

Read/Write

Read
Read
Read

Read/Write

Read

Default Value Minimum Value Maximum Value Increment

0% -30% 30% 0.1%

Analog Value – Temperature Offset

This object represents the Temperature Offset value (OFT). Note that the Units
property is writable. Changing the Units value in this object will change the Units used
by the entire device.

Property Default Value Property Data Type Access

Object Identier

Object Name
Object Type
Present Value
Status Flags
Event State
Reliability
Out Of Service
Units

Present Value: This value allows the temperature to be adjusted by a xed amount to

match another calibrated measurement.

AV11
“Temperature Offset”
ANALOG_VALUE (2)
0
0

NORMAL (0)

NO_FAULT_DETECTED(0)
FALSE (0)

Degrees-Celsius (62) or
Degrees-Fahrenheit (64)

BACnetObjectIdentier

CharacterString
BACnetObjectType
Real
BACnetStatusFlags
BACnetEventState
BACnetReliability
Boolean
BACnetEngineeringUnits

Read
Read
Read

Read/Write

Read
Read
Read

Read/Write
Read/Write

Default Value Minimum Value Maximum Value Increment

0° -30° 30° 0.1°

Analog Value – CO2 Offset

This object represents the CO2 Concentration offset value (OFC).

Property Default Value Property Data Type Access

Object Identier

Object Name
Object Type
Present Value
Status Flags
Event State
Reliability
Out Of Service
Units

Present Value: This value allows the CO2 Concentration to be adjusted by a xed
amount to match another calibrated measurement.

AV8
“CO2 Offset”
ANALOG_VALUE (2)
0
0

NORMAL (0)

NO_FAULT_DETECTED(0)
FALSE (0)

Parts-per-million (96)

BACnetObjectIdentier

CharacterString
BACnetObjectType
Real
BACnetStatusFlags
BACnetEventState
BACnetReliability
Boolean
BACnetEngineeringUnits

Read
Read
Read

Read/Write

Read
Read
Read

Read/Write

Read

Default Value Minimum Value Maximum Value Increment

0 PPM -500 PPM 500 PPM 1 PPM

Analog Value – Barometric Pressure

This object represents the typical barometric pressure at the install location (BAR).
Note that the Units property is writable. Changing the Units value in this object will
change the Units used by the entire device.

Property Default Value Property Data Type Access

Object Identier

Object Name
Object Type
Present Value
Status Flags
Event State
Reliability
Out Of Service
Units

Present Value: 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.

AV9
“Barometric Pressure”
ANALOG_VALUE (2)
1013 (29.9)
0

NORMAL (0)

NO_FAULT_DETECTED(0)
FALSE (0)
Hectopascals(133) or

Inches-of-Mercury (61)

BACnetObjectIdentier

CharacterString
BACnetObjectType
Real
BACnetStatusFlags
BACnetEventState
BACnetReliability
Boolean
BACnetEngineeringUnits

Read
Read
Read

Read/Write

Read
Read
Read

Read/Write
Read/Write

Default Value Minimum Value Maximum Value Increment

1013 hPa (29.9 inHg) 677 hPa (20.0 inHg) 1016 hPa (30.0 inHg) 1 hPa (0.1 inHg)

Binary Value – Override

This object represents the value of the override state. A press of the override button
can only set the override state to ACTIVE. The override button will not toggle the
override state. The override state can only be set to INACTIVE via BACnet. This object
supports COV subscriptions to allow easy monitoring of the override state. Every press

of the override button will send a COV notication to subscribers regardless of the
current override state. This ensures subscribers are notied even if the state is already

ACTIVE.

Property Default Value Property Data Type Access

Object Identier

Object Name
Object Type
Present Value
Status Flags
Event State
Reliability
Out Of Service

Binary Value – Use SI Units

This object represents the current system of units in use by the device (UNI).

BV1
“Override”
BINARY_VALUE (5)
0
0

NORMAL (0)

NO_FAULT_DETECTED(0)
FALSE (0)

BACnetObjectIdentier

CharacterString
BACnetObjectType
BACnetBinaryPV
BACnetStatusFlags
BACnetEventState
BACnetReliability
Boolean

Read
Read
Read

Read/Write

Read
Read
Read

Read/Write

Property Default Value Property Data Type Access

Object Identier

Object Name
Object Type
Present Value
Status Flags
Event State
Reliability
Out Of Service

Present Value: This value affects the data on the display as well as the data read from
the BACnet objects.

BV2
Use SI Units
BINARY_VALUE (5)
Region Dependent
0

NORMAL (0)

NO_FAULT_DETECTED(0)
FALSE (0)

BACnetObjectIdentier

CharacterString
BACnetObjectType
BACnetBinaryPV
BACnetStatusFlags
BACnetEventState
BACnetReliability
Boolean

Read
Read
Read

Read/Write

Read
Read
Read

Read/Write

Region Present Value UNI Value Description

North America (Default)

Europe (Default)

INACTIVE

ACTIVE

“US”

“SI”

US Customary Units

(°F, inHg, BTU/lb dry-air)

International System Units

(°C, hPa, kJ/kg dry-air)

BACnet Services

Device Communication Control Service (DM-DCC-B)

This device supports the Device Communication Control Service BIBB. The optional

time duration in minutes is also supported. This device is congured with a password

that must be provided to successfully execute this command. The password is “Dwyer”.

Reinitialize Device Service (DM-RD-B)

This device supports the Reinitialize Device Service BIBB. The supported device

states are COLDSTART and WARMSTART. All other states return error. This device
is congured with a password that must be provided to successfully execute this

command. The password is “Dwyer”.

Subscribe COV Service (DS-COV-B)

This device supports the SubscribeCOV Service BIBB to allow easy monitoring of
input data.

• Up to seven (7) concurrent subscriptions

• Conrmed and Unconrmed COV Notications

• Fixed lifetime value up to 86400 seconds (24 hours).

• Indenite lifetime supported.

MODBUS

Modbus

Communications wiring must be in a daisy-chain fashion. Star

Modbus® Functions

The CDTA and CDTC supports the following functions.

®

NOTICE

NOTICE

®

installations should comply with Modbus® Communication
Protocol over Serial Line Specication and Implementation Guide
V1.02, Modbus® Organization, Inc., 2006

connections and T connections are not permitted

Function Name Function Code

Read Holding Registers
Read Input Registers
Write Single Register

Write Multiple Registers

03
04

06
16

Modbus® Registers

Input Registers

The String data type is read as a stream of ASCII characters with the rst character
sent in the MSB of the rst register and the second character sent in the LSB of the
rst register and so on. If the string is shorter than the allotted size, the remaining

bytes will be zero padded.

INPUT REGISTERS

Register Description Data Type Range

0001

0002*

0003
0004

0005

0006

0007

0008*

0009

0010

1000 – 1009
1010 – 1015

1016 – 1018

CO2 Concentration in PPM

Relative Humidity in 0.1%

Temperature in 0.1°C or °F
Dew Point Temperature in

0.1°C or °F
Wet Bulb Temperature in

0.1°C or °F

Specic Enthalpy in 0.1 kJ/
kg dry air or BTU/lb dry air
CO2 Measurement Status

Humidity Measurement

Status

Temperature Measurement

Status

Set Point Status

Model Number String

Serial Number String
Firmware Version String

Unsigned 16bit

integer

Unsigned 16bit

integer

Signed 16bit integer
Signed 16bit integer

Signed 16bit integer

Signed 16bit integer

Unsigned 16bit

integer

Unsigned 16it integer

Unsigned 16bit

integer

Unsigned 16bit

integer
String
String
String

0 – 1000

0 – OK
1 – Not Installed
2 – Not Functional
0 – OK
1 – Not Installed
2 – Not Functional
0 – OK
1 – Not Installed
2 – Not Functional
0 – OK
1 – Not Installed
“CDTA-???0-???”

“?.?”

*Only the Series CDTA has humidity sensing capabilities.

Holding Registers

The holding registers allow the device to be completely congured 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 Value Range

0001

0002

0003

0004

0005

0006

0007*

0008

0009

0010

0500

*Only the Series CDTA has humidity sensing capabilities.

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 inHg)

±30.0%

±30.0°C/°F

See Table 3

0 – US Customary
1 – SI
0 – Do nothing
1 – Warm Reset

MAINTENANCE/REPAIR

Upon nal installation of the Series CDTA and CDTC, no routine maintenance is
required. The Series CDTA and CDTC are not eld serviceable and should be returned

if repair is needed. Field repair should not be attempted and may void 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.

Modbus® is a registered trademark of Schneider Automation, Inc.

©Copyright 2022 Dwyer Instruments, Inc. Printed in U.S.A. 1/22 FR# 444670-00

DWYER INSTRUMENTS, INC.

P.O. BOX 373 • MICHIGAN CITY, INDIANA 46360, U.S.A.

Phone: [phone]

Fax: [phone]

www.dwyer-inst.com

e-mail: [e-mail]