Dwyer Instruments GSTC Series Installation And Operating Instruction Manual

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Series GSTC Carbon Monoxide/Nitrogen Dioxide Gas Transmitter

Specifications - Installation and Operating Instructions

With LCD

he Series GSTC Carbon Monoxide/Nitrogen Dioxide Gas Transmitter

T

Without LCD

monitors the gas concentration in underground parking garages and loading docks.
The carbon monoxide transmitter is used to measure the exhaust of gasoline
engines, while the nitrogen dioxide transmitter is used for diesel engines. The
Series GSTC is compatible with either BACnet or MODBUS

rotocol, allowing the transmitter to be used with almost any building management

p

ontroller. The GSTC output is communicated over an RS-485 wire via BACnet or

c
MODBUS

®

communication protocol. To maximize the accuracy of the Series GSTC,
the sensor can be field-calibrated using the A-449 remote LCD display. When the
sensor reaches the end of its life, the display will indicate that the sensor needs to
be replaced.

BACnet and MODBUS

®

communication protocol recommend limiting the number of
nodes in any segment to 32. Therefore, the transceiver may be rated at one unit
load. Fractional loads are also acceptable. The Series GSTC accounts as an
eighth of a load on the MSTP network.

WARNING

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 national and local
electrical codes. Use copper conductors only.

NOTICE

Use electrostatic discharge precautions (e.g., use of wrist

straps) during installation and wiring to prevent equipment
damage.

NOTICE

Avoid locations where severe shock or vibration, excessive

moisture, or corrosive fumes are present.

NOTICE

Do not exceed ratings of this device, permanent damage not

covered by warranty may result.

NOTICE

The electrochemical sensors should be stored in an

environment with a minimum humidity level of 20% RH. If the
sensor dries out, replacements will not be covered under warranty, but they can be
revived by allowing them to stabilize in an environment above 40% RH for 10 days.
Once revived, they need to be recalibrated before use.

INSTALLATION

NOTICE

These are general guidelines. Local laws or ordinances will take

precedence.

• The transmitter should be mounted at normal breathing height, approximately 5
to 6 ft above the floor.

• The unit may be mounted in the horizontal or vertical position. It should be
mounted in an area that is shielded from direct contact with the elements or direct
sunlight.

• Mount in an area that will prevent the sensor from having any direct contact with
water.

• The unit should be placed in an area that will give an average of the air quality.
Do not place the unit so it will receive direct engine exhaust. Prolonged exposure
to direct engine exhaust may damage the sensor.

®

communication

Duct MountWall Mount

PECIFICATIONS

S
Sensor: Field replaceable

electrochemical, 4 years typical
lifespan.
Range: CO: 0 to 500 PPM, NO

PM.

P

utput Drift: <5% per year in air.

O
Coverage Area: 5000 to 7500 sq ft

typical.
Accuracy: CO: 2% FS, NO
at the time of calibration.
Resolution: CO: 1 PPM; NO
PPM.
Temperature Limits: -4 to 122°F (-20
to 50°C).
Storage Temperature: For best
sensor life, 32 to 68°F (0 to 20°C).
Humidity Limits: 15 to 90% RH
constant; 0 to 99% RH intermittent.
Response Time: <45 s to 90% CO,
<25 s to 90% NO

2.

Wall Mount Duct MountWall Mount

2: 10

2: 3% FS,

2: 0.1

pan and Zero Adjustment: Via

S

pushbutton, using optional A-449
display. Zero only via BACnet or
MODBUS

®

communication protocol.

Housing: UV resistant glass filled

olycarbonate.

p

utput Signals: BACnet MS/TP or

O

MODBUS

®

RTU (switch selectable)

communication protocol.
Power Requirements: 10 to 36 VDC
or isolated 21.6 to 33 VAC.
Electrical Connection: Removable
terminal block, knock outs for conduit
fitting.
Calibration: Via pushbuttons using A­449 auxiliary display. Span gas
concentration is field selectable.

Enclosure Rating: IP64.
Weight: 1 lb (0.45 kg).
Agency Approvals: CE.

Figure 1 shows the location of the wiring terminal, 8 position DIP Switch SW1, used
for configuring the RS-485 address, the 4 position DIP Switch SW2, used for
configuring hardware and software options, sensor, span and zero adjustments,
and status LEDs.

The device provides three LEDs to indicate status and activity. The LEDs are
located to the right of DIP Switch SW1. The yellow LED indicates that the unit is
sending a BACnet or MODBUS
the unit is receiving a BACnet or MODBUS
this specific device. The red LED will flash once periodically if the BACnet or
MODBUS

®

communication protocol address is set incorrectly or the red LED will

®

communication protocol. The green LED indicates

®

communication protocol addressed to

flash twice periodically if the auto serial configuration is in progress.

Span

Sensor

DIP Switch

DIP Switch

SW2

Wiring

Terminal

Figure 1

Zero

SW1

Status

LEDs

DWYER INSTRUMENTS, INC.

P.O. BOX 373 • MICHIGAN CITY, INDIANA 46360, U.S.A. Fax: [phone] e-mail: [e-mail]

Phone: [phone] www.dwyer-inst.com

TO NEXT

D

EVICE

B(+)
A(-)

P

WR

COM

TO PREVIOUS

D

EVICE

B(+)
A

(-)

P

WR

COM

ATTACH SHIELDS
T

OGETHER W/WIRE NUT

P

WRCOM A(-) B(+)

1234

B(+)
A(-)

B(+)
A(-)

COM

-+

COM

TO PREVIOUS

DEVICE

TO NEXT

DEVICE

ATTACH SHIELDS
TOGETHER W/WIRE NUT

PWRCOM A(-) B(+)

1234

all Mounting

W

. Remove the cover plugs from the face of the unit and the top cover.

1

. Disconnect the display cable from the USB connector on the main circuit board

2

if present).

(

3. Remove the desired conduit fitting knock out and install conduit fitting (not
provided).

4. Position the transmitter where it is to be mounted and mark the mounting holes
n each corner of the housing.

i

. Drill or punch out marked locations.

5

. Place the transmitter box over mounting holes on wall and align. Install wall

6

ount screws (not provided) in mounting holes.

m

7. Proceed with wiring diagrams according to Figures 3 and 4.

8. Set DIP Switches SW1 and SW2 as desired. Refer to Figure 5, Figure 6, and

Appendix I.

. Reconnect the LCD cable to the USB port on the main circuit board (if present).

9

0. Replace cover and cover plugs on the face of the unit.

1

CO:
Locate GSTC carbon monoxide transmitter about 5 ft (1.5 m) off the floor. Carbon
monoxide weighs about the same as air and distributes evenly throughout the
monitored space. Install GSTC CO alarm at least 15 to 20 ft (4.6 to 6.1 m) away

rom boiler or fuel burning heat source. Avoid extremely dusty, dirty, humid or

f

reasy areas. Do not place in direct sunlight or areas subjected to extreme

g

emperature. Do not place in turbulent air, near fans, heat vents, air conditioners,

t
air returns or open windows. Blowing air may prevent CO from reaching the CO
sensor.

NO

:

2

O

ensors should be mounted in the breathing zone, 4 to 6 ft (1.2 to 1.8 m) from

N

s

2

he floor. This is primarily because NO

t

etected in the area where people would be exposed to it, but also because 4 to 6

d
ft from the floor is an appropriate elevation to detect NO

s a poisonous gas which should be

i

2

gas.

2

Duct Mounting

Duct mounting kit includes an air flow pitot tube, air filter with barbed connections,
two short pieces of tubing, and one long piece of tubing.

igure 3 shows how to connect the GSTC in a network containing a common

F

ower supply. Use a cable containing two twisted pairs. One pair is to be used for

p

he power and common. The other pair is to be used for A(-) and B(+). Attach the

t

hields together with a wire nut. This configuration is not suitable for AC supplies.

s
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, shown in

igure 4, may be a better choice.

F

igure 3 - Common Power Supply

F

igure 4 shows how to connect the GSTC in a network containing individual local

F

upplies. Use a cable containing a single conductor and a twisted pair. The single

s
conductor is to be used for common, and the pair is to be used for A(-) and B(+).
Attach the shields together with a wire nut. Both AC and DC supplies are suitable
for this configuration.

1. Mount the pitot tube into the duct observing the flow direction marked on the pitot

tube.

2. Attach the two short pieces of tubing to the barbed connections on each side of

the air filter. See Figure 2.

3. Attach the remaining side of one of the short pieces of tubing to the barbed

connection on the transmitter.

4. Attach the remaining side of the other short piece of tubing to the high port on

the pitot tube.

5. Attach the long piece of tubing to the open barbed connection on the transmitter.

6. Attach the other end of the long tubing to the low port on the pitot tube.

Figure 2

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

Building Automation and Control Networks, American Society of Heating,

BACnet installations should comply with ANSI/ASHRAE
Standard 135-2010 BACnet A Data Communication Protocol for

Refrigerating and Air-Conditioning Engineers, Inc., 2010.

NOTICE

Specification and Implementation Guide V1.02, MODBUS

NOTICE

NOTICE

MODBUS®communication protocol installations should comply
with MODBUS

®

communication protocol over Serial Line

Communication wiring must be in a daisy-chain fashion. Star
connections are not permitted.

Cable shield must be connected to earth ground at one location
only.

®

Organization, Inc., 2006.

Figure 4 - Local Power Supply

All devices in the network should be daisy-chained. Star connections and T
connections are not permitted.

The A(-) and B(+) lines must be terminated at both ends with a 120 ohm resistor.
If the GSTC is an end device it has an on-board resistor that may be used. See
Table 1 to enable it.

The network must be biased properly. If needed, there are bias resistors on-board
the GSTC. No more than two sets of bias resistors should be enabled in the
network. See Table 1 to enable them.

ip Switch Configurations

D

se DIP Switch SW1 (see Figure 5) to configure the RS-485 address of the device.

U

valid address depends on the protocol selected. Valid BACnet addresses range

A

rom 1 to 127. Valid MODBUS

f

247. By default, the device is shipped with MODBUS

®

ommunication protocol addresses range from 1 to

c

®

communication protocol
selected and the address set to 127, as shown in Figure 5. A valid and unused
address should be set before connecting to an existing network. See Appendix I to

onfigure the required address using DIP Switch SW1. The device will not function

c

roperly if an invalid address is set. During the power up sequence, the LCD (if

p

resent) will display the RS-485 address as the primary value and either “BAC” to

p

ndicate BACnet or “MOD” to indicate MODBUS

i

®

ommunication protocol as the

c
primary text. If the RS-485 address is invalid, the invalid address is shown as the
primary value with “ERR” as the primary text, and the red LED will periodically blink
once.

o activate auto serial configuration, set a valid RS-485 address using DIP Switch

T

W1, connect the serial bus, common and power wires, and apply power. The

S

evice will power up and begin examining the serial bus for communication.

d

When the device is installed offline or away from the main network, it is necessary
to generate the appropriate traffic in order to configure the serial communication
whether BACnet or MODBUS

onfiguration is in progress, the device may not respond. The device may require

c

ultiple read requests to complete the serial configuration process.

m

he auto serial configuration process is completed once a message addressed to

T

®

communication protocol is selected. While the serial

the device is received and processed successfully. If the serial configuration of the
bus changes, a power cycle of the device is required to restart the auto serial
configuration process.

ore detailed information for BACnet protocol can be found in Appendix II, and

M

nformation for MODBUS

i

®

ommunication protocol can be found in Appendix III.

c

MENU

The menu is only shown if a display is present. Figure 7 below outlines the display
components. To enter the menu, press and hold both the SPAN and ZERO

ushbuttons for at least 3 seconds. The menu descriptions and list of the available

p

alues for each standard menu item is shown on in Table 3. Table 4 lists the

v

vailable values for each manual menu item.

a

igure 5

F

Use DIP Switch SW2 (see Figure 6) to configure other hardware and software

ptions. Table 1 shows available options. Table 2 shows supported configurations

o

or either BACnet or MODBUS

f

®

ommunication protocol.

c

Figure 6

Switch

1 - Protocol
2 - B(+) Bias Resister
3 - A(-) Bias Resister
4 - Terminating Resister

On

MODBUS

®

511Ω Pull-up to 5V
511Ω Pull-down to GND
120Ω between A(-) and B(+)

Off

BACnet
Pull-up not connected
Pull-down not connected
Open

Table 1: Dip Switch SW2 Functions

Auto Serial Configuration

Use the auto serial configuration to enable the device to determine the baud rate,
parity, and stop bits directly from the serial traffic. After a valid RS-485 address is
chosen, the GSTC can be quickly and easily deployed. The auto serial
configuration procedure assumes a serial configuration appropriate to the chosen
protocol, shown in Table 2. Otherwise, the serial communication must be
configured manually in the setup menu.

Stop Bits

Protocol

BACnet

Supported Baud Rates

9600

Data Size

Parity

None

1

19200

1

MODBUS

®

38400
57600
76800

8

Even
Odd
None

2

115200

Table 2: Supported Configurations

Text

econdary

S

isplay

D

Text

Primary

Display

Numeric

Figure 7

Standard Menu Descriptions

BAC or MOD: Displays the RS-485 address
CAL: Start user CO or NO2 calibration process
AUT: Auto serial configuration enabled
RST: Reset settings to factory default

Manual Menu Descriptions

BAU: Baud rate selection (only available if AUT = OFF)
PAR: Parity selection (only available if AUT = OFF)
STP: Stop bits selection (only available if AUT = OFF)

Menu Navigation

A menu flowchart, located in Appendix IV, illustrates the navigation process.

1. Press and hold the SPAN pushbutton while in the menu to move to the previous
menu item.

2. Press and hold the ZERO pushbutton while in the menu to move to the next
menu item.

3. Press and hold both the SPAN and ZERO pushbuttons for 5 seconds to activate
the current menu item. In the lower left corner of the display “SET” is shown to
indicate a setting change.

4. Press and hold either the SPAN or ZERO pushbutton to change the setting.

5. Press and hold both the SPAN and ZERO pushbuttons for 5 seconds to accept
the setting.

6. After 30 seconds of inactivity, the display will return to normal operation.

Menu Name

BAC or MOD
CAL
AUT

RST

Value

xxx ADR
xxx PPM
ON
OFF
NO
YES

Description

RS-485 address (view only)
Current CO or NO2 concentration
Auto-baud will start and return to the main menu
Starts the manual serial configuration menu sequence

Will reset settings to factory default

Table 3: Standard Menu Options

enu Name

M

V

alue

D

escription

9600
19200
38400

AU

B

PAR

5

6800

7

15200

1

VE

E

Only available if AUT = OFF

ODD

nly available if AUT = OFF

O

7600

NON
1

STP

Only available if AUT = OFF

2

Table 4: Manual Menu Options

ENSOR REPLACEMENT

S

replacement sensor is available from Dwyer Instruments, Inc.

A

or CO, order part number: A-505.

F
For NO

, order part number: A-506.

2

ARNING

W

ensors contain acid and are harmful if handled improperly. Do

S
not attempt to open sensors. Sensors should be disposed of

according to local laws.

Replacing The Sensor

1. Remove the cover plugs from the face of the unit and top cover. Locate the
sensor, see Figure 1. The sensor is mounted on three pin sockets. The circuit
board is either labeled “CO SENSOR” or “NO2 SENSOR” underneath the sensor.

. Remove and discard the used sensor.

2

. Remove the shorting wire spring located at the bottom of the new sensor.

3

. Install the new sensor into the three pin sockets.

4

5. The unit must be re-calibrated whenever a new sensor is installed.

6. Allow 30 minutes for the unit to come to temperature equilibrium prior to
calibration. The unit has internal temperature compensation, and the sensor must
be at the same temperature as the unit to calibrate properly.

CALIBRATION

Figure 8, located after Appendix III, shows how to set up a GSTC for calibration
with an auxiliary display. An auxiliary display is required for calibration unless an
LCD model of the GSTC was purchased. The procedure in Appendix IV shows how
to set the range, and calibrate the span and zero adjustments.

MAINTENANCE/REPAIR

Upon final installation of the Series GSTC, no routine maintenance is required with
the exception of sensor replacement and calibration. As with all electrochemical
type gas sensors, routine calibration is required. It is recommended that units be
re-calibrated at 6 month intervals, to maintain the published accuracy, or as
required by local ordinances or other requirements. The units will maintain 5%
accuracy if they are re-calibrated at 12 month intervals.

Except for the sensor replacement and calibration, the Series GSTC is not field
serviceable and should be returned if repair is needed. Field repair should not be
attempted and may void warranty.

he address of the transmitter in Figure 9 is 127. This final value is determined by

T

dding the individual values of the DIP switches together. The values for each DIP

a

witch are shown below in Table 5. When adding the individual values for Figure 9,

s

+64+32+16+8+4+2+1=127, which is the correct factory setting.

0

Switch Positions

ddress Value

A

1

2826

1

433

658647281

241

Table 5: DIP Switch Values

nother example would be if the desired address was 53. The only DIP switches

A
in the “ON” position would be switches 3, 4, 6, and 8 as shown in Figure 10 below.
By adding the individual values of each switch in the “ON” position,
0+0+32+16+0+4+0+1=53, the desired address is obtained.

Figure 10

NOTICE

The minimum possible address would be 0 when all DIP

switches are in the “OFF” position, and the maximum possible
address would be 255 when all DIP switches are in the “ON” position. When BACnet
protocol is selected the transmitter only has valid address from 1 to 127. When
M
f

®

ODBUS

ommunication protocol is selected the transmitter only has valid address

c

rom 1 to 247. Any address outside the selected protocol’s range will give an error.

Appendix II: BACnet Protocol

The GSTC supports objects that are listed below. Table 6 and Table 7 outlines
each item.

Object Type

Device
Analog Input

Dynamically
Creatable

No
No

Dynamically
Deletable

No
No

Object
Identifier

607xxx
AI1

Object
Name

GSTC
CO Concentration

NO2 Concentration
Binary Value
Date Value

No
No

No
No

BV1
DV1
DV2

Zero Sensor

Calibration Date

Replace Sensor Date

Table 6: Supported BACnet Objects

WARRANTY/RETURN

Refer to “Terms and Conditions of Sales” in our catalog and on our website.
Contact customer service to receive a Return Goods Authorization number before
shipping the product back for repair. Be sure to include a brief description of the
problem plus any additional application notes.

Appendix I: Setting the RS-485 Address

The address assignment is determined by adding the values for each of the
switches that are in the “ON” position. The transmitter comes from the factory with
all of the DIP switches in the “ON” position, except position 1 as shown in Figure 9
below.

Figure 9

roperty Data

efault

D

Property

Object Identifier

bject Name

O

bject Type

O

System Status

Vendor Name

endor Identifier

V

odel Name

M

Firmware Revision
Application Software
Version

ocation

L

escription

D

Protocol Version
Protocol Revision
Protocol Services

upported

S

rotocol Object Types

P

upported

S
Object List
Maximum APDU Length
Accepted
Segmentation

upported

S

PDU Timeout

A
Number of APDU
Retries
Max Master
Max Info Frames
Devices Address
Binding
Database Revision
Serial Number (1000)

The default object identifier is 607xxx, where xxx is replaced by the address set by
the DIP Switch SW1. The object identifier value will change as the address
changes. When a specific object identifier is written via BACnet, that value is stored
and changes to the address will no longer affect the object identifier. The object
name reflects the current object identifier. When a specific object name is written
via BACnet, that value is stored and changes to the object identifier will no longer
affect the object name.

Table 8 outlines the Analog Input (AI1) object which represents the current CO or
NO2 concentration reading in parts per million.

Property

Object
Identifier
Object Name

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

Default Value

AI1

“CO Concentration” or
“NO2 Concentration”
ANALOG_INPUT (0)
Current reading
0
NORMAL (0)
NO_FAULT_DETECTED(0)
FALSE (0)

Parts-per-million (96)

Value

607xxx

GSTC 607xxx”

“

EVICE (8)

D

Operational (0)

“Dwyer

nstruments, Inc”

I

07

6

GSTC-C” or

“

GSTC-N”

“
“?.?”
“?.?”

”

“

CO Detector” or

“
“NO2 Detector”
1
12
See pics

ee Table 2

S

See Table 2
128

NO_SEGMENTAT

ON (3)

I
0
0

127
1
Empty

1
“xxxxxx”

Table 7: Object Properties

Table 8: Analog Input

P
Type

BACnetObjectId
entifier

haracterString

C

32)

(

ACnetObjectT

B

pe

y
BACnetDeviceS
tatus
CharacterString

nsigned

U

haracterString

C

CharacterString
CharacterString

haracterString

C

32)

(

haracterString

C
(32)
Unsigned
Unsigned
BACnetServices

upported

S

ACnetObjectT

B

pesSupported

y
BACnetArray
Unsigned

BACnetSegmen

ation

t

nsigned

U
Unsigned

Unsigned
Unsigned
BACnetAddress
Binding
Unsigned
CharacterString

Property Data Type

BACnetObjectIdentifier

CharacterString

BACnetObjectType
Real
BACnetStatusFlags
BACnetEventState
BACnetReliability
Boolean

BACnetEngineeringUnits

Access

Read/Write

R

R

Read

Read

R
R

Read
Read

R

R

Read
Read
Read

R

Read
Read

Read

R
Read

Read/Write
Read
Read

Read
Read

ead/Write

ead

ead
ead

ead/Write

ead/Write

ead

ead

Access

Read

Read

Read
Read
Read
Read
Read
Read/Write

Read

able 9 outlines the Binary Value (BV1) object which allows the sensor to be

T

emotely zeroed. When set to “ACTIVE”, the zero function will attempt to

r

ecalibrate the zero point of the sensor.

r

roperty

P

bject

O
Identifier
Object Name

bject Type

O

resent Value

P

tatus Flags

S

vent State

E
Reliability
Out of
Service

Table 10 outlines the Date Value (DV1) object which stores the date when the
sensor was last calibrated. Since the GSTC does not track time this value must be
updated manually after calibration is performed in the field.

Property

Object
Identifier
Object Name

Object Type
Present Value

tatus Flags

S

vent State

E

eliability

R
Out of
Service

Table 11 outlines the Replace Sensor Date (DV2) object which stores the
suggested sensor replacement date. It is recommended to replace the sensor at
specific intervals because the sensor degrades over time. The GSTC does not
track time so this value must be updated manually after the sensor is replaced in
the field.

Property

Object
Identifier
Object Name

Object Type
Present Value
Status Flags
Event State
Reliability
Out of
Service

efault Value

D

V1

B

“Zero Sensor”

INARY VALUE (5)

B

0
0
NORMAL (0)
NO FAULT DETECTED (0)
FALSE (0)

Table 9: Binary Value

Default Value

DV1

“Calibration Date”

DATE VALUE (42)
????

F,F,F,F}

{

ORMAL (0)

N

O FAULT DETECTED (0)

N
FALSE (0)

Table 10: Date Value

Default Value

DV2

“Replace Sensor Date”

DATE VALUE (42)
????
{F,F,F,F}
NORMAL (0)
NO FAULT DETECTED (0)
FALSE (0)

Table 11: Replace Sensor Date

roperty Data Type

P

ACnetObjectIdentifier

B

CharacterString

ACnetObjectType

B

eal

R

ACnetStatusFlags

B

ACnetEventState

B
BACnetReliability
Boolean

Property Data Type

BACnetObjectIdentifier

CharacterString

BACnetObjectType
BACnetBinaryPV

ACnetStatusFlags

B

ACnetEventState

B

ACnetReliability

B
Boolean

Property Data Type

BACnetObjectIdentifier

CharacterString

BACnetObjectType
BACnetBinaryPV
BACnetStatusFlags
BACnetEventState
BACnetReliability
Boolean

ccess

A

ead

R

Read

ead

R

ead

R

ead

R

ead

R
Read
Read/Write

Access

Read

Read

Read
Read/Write

ead

R

ead

R

ead

R
Read/Write

Access

Read

Read

Read
Read/Write
Read
Read
Read
Read/Write

ACnet Services

B

he GSTC supports the Device Communication Control Service BIBB. The option

T

ime duration in minutes is also supported. This device is configured with a

t

assword that must be provided to successfully execute the command. The

p
password is “Dwyer”.

The GSTC also supports the Reinitialize Device Service BIBB. The supported

evice states are “COLDSTART” and “WARMSTART”. All other states return an

d

rror. This device is configured with a password that must be provided to

e

uccessfully execute the command. The password is “Dwyer”.

s

Appendix III: MODBUS

®

Communication Protocol

The GSTC supports functions and input registers that are listed below. Table 12 ,
Table 13, and Table 14 outline each item.

unction Name

F

ead Holding Registers

R

ead Input Registers

R
Write Single Register
Write Multiple Registers

Table 12: Supported MODBUS

he string data type is read as a stream of ASCII characters with the first character

T

unction Code

F

3

0

4

0
06
16

®

Functions

sent in the MSB of the first register and the second character sent in the LSB of the
first register and so on. If the string is shorter than the allotted size, the remaining
bytes will be zero padded.

egister

R

001

0

escription

D

O or NO2 Concentration

C
in PPM

ata Type

D

nsigned 16 bit

U
integer

ange

R

– 500 PPM CO,

0
0 – 100 (0 – 10.0)
PPM NO2

1000-1009

Model Number String

String

“GSTC-C” or

“GSTC-N”
1010-1013
1014-1017

Serial Number String
Firmware Version String

String
String

“xxxxxx”

“?.?”

Table 13: Input Registers

Register

0001
0500

Description

Zero Sensor
Reboot device

Data Type

Unsigned 16bit integer
Unsigned 16bit integer

Value

0-1
0-1

Range

0 or 1
0 - Do Nothing
1 - Warm Reset

Table 14: Holding Registers

Writing 1 to the Zero Sensor register will re-zero the sensor just as if the user has
pressed the zero pushbutton.

The Reboot Device register allows a MODBUS

®

communication protocol 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
approximately 5 seconds after the command was received. Writing a value of 0 to
this register has no effect.

Figure 8

ADR

PPM

MOD

CO

SEN

OK

PPM

PPM

CAL

CAL

CAL

CAL

CO

SCROLL

SCROLL

SCROLL

S

CROLL

AUT

K

K

AUT

AUT

AUT

AUT

AUT

BAU

B

AU

SCROLL

S

CROLL

S

CROLL

SCROLL

SCROLL

SCROLL

SCROLL

SCROLL

SCROLL

S

CROLL

PAR

PAR

PAR

STP STP

S

ET BAUD RATE

SET PARITY

SET STOP BITS

RST

RST

RST

N

OTE - WHEN IN THE MENU, THE

D

ISPLAY WILL RETURN TO THE
HOME POSITION IF NO KEY IS
PRESSED WITHIN 30 SECONDS.

HOME POSITION, UNIT READS GAS
CONCENTRATION PPM

P

RESS AND HOLD ZERO AND SPAN

K

EYS FOR 5 SECODNS TO ENTER

T

HE MAIN MENU.

MODBUS/BACNET ADDRESS.
V

IEWABLE ONLY.

CALIBRATION
M

ODE

P

RESS ZERO AND SPAN TO ENTER CALIBRATION MODE

PRESS THE ZERO KEY FOR 5 SECONDS. THE
Z

ERO VALUE IS STORED AND THE DISPLAY

S

EQUENCES TO THE SPAN GAS CALIBRATION VALUE

PRESS AND HOLD THE SPAN KEY FOR 5 SECONDS

DISPLAY READS “CAL” THEN “PASS” AND RETURNS TO HOME POSITION

I

F THE SENSOR OUTPUT IS NO LONGER

S

UFFICIENT FOR CALIBRATION, THEN

T

HE DISPLAY READS “BAD SEN”. THE

S

ENSOR MUST BE REPLACED

P

RESS AND HOLD ZERO AND SPAN UNTIL

“

SET” TURNS OFF

TO ADJUST THE DISPLAY TO SET
THE DESIRED SPAN CALIBRATION VALUE,

P

RESS THE DIGIT KEY TO SCROLL

T

HROUGH THE DIGITS. THE DIGITS WILL

BLINK AS THEY ARE SELECTED.

A

DJUST THE VALUE OF THE DIGIT

U

SING THE VALUE KEY

H

OOK UP THE UNIT TO THE SPAN CALIBRATION GAS
USING THE CALIBRATION ADAPTER A-507AS SHOW IN FIG. 8
S

PAN GAS FLOW IS TO BE BETWEEN 0.5 TO 10. SLPM.
A

LLOW GAS TO FLOW FOR AT LEAST 3 MINUTES.

PLACE THE UNIT IN AN AREA THAT CONTAINS FRESH
A

IR (NO CO OR NO2 GAS). ALLOW 3 MINUTES TO

S

TABILIZE.

C

OMMUNICATION

S

ETTINGS
FACTORY SETTING IS
A

UTO BAUD ON.

P

RESS AND HOLD ZERO AND SPAN UNTIL

“

SET” TURNS ON

PRESS ZERO OR SPAN TO SWITCH
B

ETWEEN AUTO BAUD ON OR OFF

AUTOBAUD MUST BE SET TO “NO” TO SET
B

AUDRATE, PARITY AND STOP BIT SETTINGS

P

RESS AND HOLD ZERO AND SPAN UNTIL

“SET” TURNS OFF

PRESS AND HOLD ZERO AND SPAN UNTIL
“

SET” TURNS OFF

U

SING ZERO AND SPAN KEYS, SET BAUDRATE

TO DESIRED VALUE

P

RESS AND HOLD ZERO

A

ND SPAN UNTIL

“SET” TURNS OFF

P

RESS ZERO OR SPAN TO SWITCH

B

ETWEEN NO PARITY OR EVEN OR

ODD PARITY

PRESS AND HOLD ZERO AND SPAN UNTIL
“

SET” TURNS ON

PRESS AND HOLD ZERO AND SPAN UNTIL
“SET” TURNS ON PRESS AND HOLD ZERO AND SPAN UNTIL

“SET” TURNS OFF

USING ZERO AND SPAN KEYS, SET STOP BIT
TO 1 OR 2

IF RESET IS SET TO YES, PRESSING ZERO AND SPAN
WILL CAUSE A FACTORY RESET, AND DISPLAY WILL
RETURN TO THE HOME POSITION

IF RESET IS SET TO NO, PRESSING ZERO AND SPAN

PRESS ZERO OR SPAN TO SWITCH
BETWEEN YES OR NO

PRESS AND HOLD ZERO AND
SPAN UNTIL “SET” TURNS ON

RESET UNIT
TO FACTORY
DEFAULTS

SCROLL TO TOP
MENU, MODBUS/BACNET
ADDRESS

SPAN
D

IGIT

Z

ERO

V

ALUE

S

PAN

D

IGIT

ZERO

VALUE

ZERO

VALUE

S

PAN

DIGIT

ZERO

V

ALUE

SPAN
D

IGIT

Z

ERO

VALUE

S

PAN

D

IGIT

SPAN
DIGIT

Z

ERO

V

ALUE

Z

ERO

VALUE

S

PAN

DIGIT

Z

ERO

VALUE

S

PAN

D

IGIT

ZERO
V

ALUE

SPAN
D

IGIT

Z

ERO

VALUE

S

PAN

DIGIT

ZERO

VALUE

Z

ERO

V

ALUE

SPAN
D

IGIT

ZERO

V

ALUE

SPAN
D

IGIT

SPAN
D

IGIT

ZERO

VALUE

ZERO

V

ALUE

SPAN
D

IGIT

ZERO

VALUE

SPAN
DIGIT

ZERO
VALUE

SPAN
DIGIT

SPAN
DIGIT

ZERO
VALUE

ZERO
VALUE

SPAN
DIGIT

ZERO

VALUE

SPAN
DIGIT

SPAN
DIGIT

ZERO
VALUE

SPAN
DIGIT

ZERO
VALUE

ZERO
VALUE

SPAN
DIGIT

ZERO

VALUE

SPAN
DIGIT

SPAN
DIGIT

ZERO

VALUE

ppendix IV: Menu Flowchart and Calibration

A

©Copyright 2017 Dwyer Instruments, Inc. Printed in U.S.A. 1/17 FR# 443872-00 Rev. 5

DWYER INSTRUMENTS, INC.

Phone: [phone] www.dwyer-inst.com

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