Dwyer Instruments GSTA, GSTC Operating Manual

Bulletin AQ-GSTC

3-23/64

®

Series GSTC Carbon Monoxide/Nitrogen Dioxide Gas Transmitter

Specications - Installation and Operating Instructions

Wall mount

with LCD

The Series GSTC Carbon Monoxide/Nitrogen Dioxide Gas Transmitter 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
to be used with almost any building management controller. The GSTC output is
communicated over an RS-485 wire via BACnet or Modbus

To maximize the accuracy of the Series GSTC, the sensor can be eld-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
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

accordance with the job wiring diagram and in accordance with national and local
electrical codes. Use copper conductors only.

NOTICE

NOTICE

NOTICE

NOTICE

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

• The transmitter should be mounted at normal breathing height, approximately 5 to 6

ft above the oor.

• 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 protocol recommend limiting the number of

Disconnect power supply before installation to prevent electrical
shock and equipment damage. Make sure all connections are in

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

Avoid locations where severe shock or vibration, excessive
moisture, or corrosive fumes are present.

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

The electrochemical sensors should be stored in an environment
with a minimum humidity level of 20% RH. If the sensor dries out,

These are general guidelines. Local laws or ordinances will take
precedence.

Wall mount

without LCD

®

communication protocol, allowing the transmitter

®

communication protocol.

Duct mount

3-45/64

[94.06]

3-1/8

[107.95]

4-17/32
[115.09]

5-7/64

[129.78]

SPECIFICATIONS

Sensor: Field replaceable electrochemical, 4 years typical lifespan.
Range: CO: 0 to 500 PPM, NO2: 10 PPM.

Output Drift: <5% per year in air.
Coverage Area: 5000 to 7500 sq ft typical.
Accuracy: CO: 2% FS, NO2: 3% FS, at the time of calibration.
Resolution: CO: 1 PPM; NO2: 0.1 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% NO2.

Span and Zero Adjustment: Via pushbutton, using optional A-449 display. Zero
only via BACnet or Modbus

Housing: UV resistant glass lled polycarbonate.
Output Signals: BACnet MS/TP or Modbus

communication protocol.

Power Requirements: 10 to 36 VDC or isolated 21.6 to 33 VAC.
Electrical Connection: Removable terminal block, knock outs for conduit tting.
Calibration: Via pushbuttons using A-449 auxiliary display. Span gas
concentration is eld 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

conguring the RS-485 address, the 4 position DIP Switch SW2, used for conguring

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
BACnet or Modbus

red LED will ash once periodically if the BACnet or Modbus
address is set incorrectly or the red LED will ash twice periodically if the auto serial
conguration is in progress.

®

communication protocol. The green LED indicates the unit is receiving a

Span

Sensor

DIP Switch

SW2

Wiring

Terminal

®

communication protocol.

®

communication protocol addressed to this specic device. The

2-15/64

[56.75]

Duct mountWall mount

®

RTU (switch selectable)

[85]

2-55/64

[73]

2-15/64

[57]

3-59/64

[100]

®

communication protocol

Zero

DIP Switch

SW1

Status

LEDs

DWYER INSTRUMENTS, INC.

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

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

Phone: [phone]

Fax: [phone]

Figure 1

www.dwyer-inst.com

e-mail: [e-mail]

Wall Mounting

TO

PWRCOM A(-)B(+)

TO

NEXT

PWRCOM A(-) B(+)

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

2. Disconnect the display cable from the USB connector on the main circuit board (if
present).

3. Remove the desired conduit tting knock out and install conduit tting (not

provided).

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

5. Drill or punch out marked locations.

6. Place the transmitter box over mounting holes on wall and align. Install wall mount
screws (not provided) in mounting holes.

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.

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

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

CO:

Locate GSTC carbon monoxide transmitter about 5 ft (1.5 m) off the oor. 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 from
boiler or fuel burning heat source. Avoid extremely dusty, dirty, humid or greasy areas.
Do not place in direct sunlight or areas subjected to extreme temperature. Do not place
in turbulent air, near fans, heat vents, air conditioners, air returns or open windows.
Blowing air may prevent CO from reaching the CO sensor.

2:

NO

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

NO

oor. This is primarily because NO

2 is a poisonous gas which should be detected in

the area where people would be exposed to it, but also because 4 to 6 ft from the oor

is an appropriate elevation to detect NO

2 gas.

Duct Mounting

Duct mounting kit includes an air ow pitot tube, air lter with barbed connections, two

short pieces of tubing, and one long piece of tubing.

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

tube.

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

air lter. 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 3 shows how to connect the GSTC in a network containing a common power
supply. Use a cable containing two twisted pairs. One pair is to be used for the power
and common. The other pair is to be used for A(-) and B(+). Attach the shields together

with a wire nut. 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, shown in Figure 4, may be a

better choice.

1234

PREVIOUS

DEVICE

B(+)
A(-)
PWR

COM

ATTA CH SHIELDS
TOGETHER W/WIRE NUT

TO NEXT

DEVICE

B(+)
A(-)
PWR

COM

Figure 3 - Common Power Supply

Figure 4 shows how to connect the GSTC in a network containing individual local
supplies. Use a cable containing a single conductor and a twisted pair. The single
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 conguration.

1234

PREVIOUS

DEVICE

B(+)
A(-)

COM

TO

DEVICE

B(+)
A(-)
COM

-+

ATTA CH SHIELDS
TOGETHER W/WIRE NUT

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.

WIRING

NOTICE

Figure 2

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

BACnet installations should comply with ANSI/ASHRAE Standard

135-2010 BACnet A Data Communication Protocol for Building
Automation and Control Networks, American Society of Heating, Refrigerating and
Air-Conditioning Engineers, Inc., 2010.

®

communication protocol installations should comply with

NOTICE

and Implementation Guide V1.02, Modbus

NOTICE

Modbus

®

communication protocol over Serial Line Specication

Modbus

®

Organization, Inc., 2006.

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

connections are not permitted.

NOTICE

Cable shield must be connected to earth ground at one location

only.

Dip Switch Congurations

NETWORK BIAS

PROTOCOL NETWORK TERMINATION

Use DIP Switch SW1 (see Figure 5) to congure the RS-485 address of the device. A

valid address depends on the protocol selected. Valid BACnet addresses range from
1 to 127. Valid Modbus
default, the device is shipped with Modbus

®

communication protocol addresses range from 1 to 247. By

®

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 congure the required

address using DIP Switch SW1. 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 and either “BAC” to indicate BACnet or “MOD” to
indicate Modbus

®

communication protocol as the 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.

ON

1 2 3 4 5 6 7 8

Figure 5

To activate auto serial conguration, set a valid RS-485 address using DIP Switch

SW1, connect the serial bus, common and power wires, and apply power. The device
will power up and begin examining the serial bus for communication.

When the device is installed ofine or away from the main network, it is necessary to
generate the appropriate trafc in order to congure the serial communication whether

BACnet or Modbus

®

communication protocol is selected. While the serial conguration

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

requests to complete the serial conguration process.

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

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

®

communication protocol can be found in Appendix III.

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 pushbuttons
for at least 3 seconds. The menu descriptions and list of the available values for each
standard menu item is shown on in Table 3. Table 4 lists the available values for each
manual menu item.

Use DIP Switch SW2 (see Figure 6) to congure other hardware and software options.
Table 1 shows available options. Table 2 shows supported congurations for either

BACnet or Modbus

®

communication protocol.

ON

1 2 3 4

Figure 6

DIP SWITCH SW2 FUNCTIONS
Switch On Off

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

®

Modbus

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

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

Table 1

Auto Serial Conguration

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

setup menu.

SUPPORTED CONFIGURATIONS
Protocol Supported Baud Rates Data Size Parity Stop Bits

BACnet 9600

19200

®

Modbus

38400
57600
76800

8

None 1

Even
Odd
None 2

1

115200

Table 2

Text

Secondary

Display

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 conguration 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 owchart, 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.

STANDARD MENU OPTIONS
Menu Name Value Description

BAC or MOD xxx ADR RS-485 address (view only)
CAL xxx PPM Current CO or NO2 concentration
AUT ON Auto-baud will start and return to the main menu

OFF Starts the manual serial conguration menu sequence

RST NO

YES Will reset settings to factory default

Table 3