ACI VOC-DUCT Gas and Specialty Sensors Instruction Manual

: June 9, 2024
: ACI

Table of Contents

ACI VOC-DUCT Gas and Specialty Sensors
Mounting Instructions
Wiring Instructions
Device Configuration Through Modbus RTU
GENERAL INFORMATION
- WIRING INSTRUCTIONS PRECAUTIONS
DEVICE CONFIGURATION THROUGH MODBUS RTU
MODBUS RTU MAP
PRODUCT SPECIFICATIONS
WARRANTY
References
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ACI VOC-DUCT Gas and Specialty Sensors

The VOC Duct is a device used to detect and measure concentrations of organic solvents, ammonia, silicone vapour or cigarette smoke in order to avoid poisoning the sensitive layer. The device comes with mounting instructions and wiring instructions that must be followed for proper installation and usage.

Mounting Instructions

The device can be mounted in two ways:

Option 1: Flange and Seal Installation

Drill a 0.75(19mm) hole into the duct.
Install the seal ring and the flange onto the duct.
Insert the probe into the duct.
Screw to lock the whole enclosure on the flange.

Option 2: Enclosure Mounting

Drill a 0.75(19mm) hole into the duct.
Insert the probe with the seal ring into the duct.
Screw the enclosure on the duct directly.

Make sure all sampling holes on the probe are inserted into the duct, and the direction shows on the front cover should be the same as air flow in the duct. All seal rings should be applied properly to ensure the entire enclosure and probe are air tight.

Wiring Instructions

ACI recommends 16 to 26 AWG twisted pair wires or shielded cable for all transmitters. ACI recommends using BELDEN 3105 for communication (Modbus) wiring. This wire has 120 ohm input impendence. The terminal blocks allow for (1) or (2) wires to be connected in each position for daisy chaining. Daisy chain the RS-485 wiring and do not use Star or T wiring. Avoid running communication wires next to AC line voltage wires. These can be sources of noise that can affect signal quality.

Jumper Settings

Make sure the jumper settings are configured as shown in Figure 9:

V+ = (+) 24VDC/VAC
V- = (-)
GND = Ground
OUT = Analog Output Signal
A = Modbus RS485 (+)
B = Modbus RS485 (-)

Device Configuration Through Modbus RTU

The Modbus Remote Terminal Unit (RTU) data link protocol uses EIA-485 as a two-wire, daisy chain network. A branch is a discrete chain of devices connected to a controller. The max number of devices per segment is (32), as per the Modbus specifications. 4000 ft (1219.2 m) is the maximum recommended length for a segment, which includes all devices from the controller to the last device in the daisy chain.

GENERAL INFORMATION

VOCs are emitted as gases from certain solids or liquids, such as building materials and furnishings, ffice equipment, cleaners and disinfectants, etc. These types of contaminants directly affect indoor air quality and occupant comfort. Measuring and communicating VOC levels back to the BAS will help users adjust ventilation to maintain proper IAQ levels. These units utilize a high-performance metal oxide sensor and will output TVOC levels in a range from 0-1000 ppb. All units come equipped with both analog and RS485 Modbus RTU outputs easily interface into existing BAS systems.

IMPORTANT PRECAUTIONS
Read the following instructions carefully before using the indoor air quality sensor described in this document to avoid erroneous readings and to prevent the device from permanent damage.

The sensor must not be exposed to high concentrations of organic solvents, ammonia, silicone vapour or cigarette-smoke in order to avoid poisoning the sensitive layer.

MOUNTING INSTRUCTIONS
For optimal temperature readings, follow these tips:

Duct probe should be placed (3) to (4) duct segments down from any bend or obstructions and away from 90° bends.
Mount the sensor on the top or sides of duct work; mounting on the bottom risks damage due to moisture.

First, assemble the separated probe on the bottom of enclosure as Fig. 2 and Fig. 3. Insert the seal ring properly and then insert the probe, screw according to the direction indication to the end.

FIGURE 1: ENCLOSURE DIMENSIONS ACI VOC-DUCT-Gas-and-Specialty-Sensors-
fig-1 FIGURE 2: DUCT COMPONENTS FIGURE 3: ATTACHING SAMPLE PROBE FIGURE 4: FLANGE AND SEAL INSTALLATION FIGURE 5: DUCT MOUNT FIGURE 6: FLANGE MOUNTING DIMENSIONS FIGURE 7: ENCLOSURE MOUNTING

Duct sensor mounting has two options. Make sure all sampling holes on the probe are inserted into the duct, and the direction shows on the front cover should be the same as air flow in the duct. All seal rings should be applied properly to ensure the entire enclosure and probe are air tight

Option #1: Install the flange and seal flrst, then insert the probe and enclosure according to Fig. 4 and Fig 5. Drill a 0.75”(19mm) hole into the duct, then install the seal ring and the flange onto the duct. Then insert the probe into, screw to lock the whole enclosure on the flange

Option #2: Install the enclosure directly into the duct as shown in Fig 7. Drill a 0.75”(19mm) hole into the duct. Insert the probe with the seal ring, and screw the enclosure on the duct directly.

Refer to the wiring instructions to make necessary connections. After wiring, attach the cover to the base and tighten the enclosure screws.

WIRING INSTRUCTIONS PRECAUTIONS

DO NOT RUN THE WIRING IN ANY CONDUIT WITH LINE VOLTAGE (24/120/230VAC).
Remove power before wiring. Never connect or disconnect wiring with power applied.
It is recommended that you use an isolated UL-listed Class 2 transformer when powering the unit with 24 VAC. Failure to wire the devices with the correct polarity when sharing transformers may result in damage to any device powered by the shared transformer.
IF THE 24 VDC OR 24VAC POWER IS SHARED WITH DEVICES THAT HAVE COILS SUCH AS RELAYS, SOLENOIDS, OR OTHER INDUCTORS, EACH COIL MUST HAVE AN MOV, DC/AC TRANSORB, TRANSIENT VOLTAGE SUPPRESSOR (ACI PART: 142583), OR DIODE PLACED ACROSS THE COIL OR INDUCTOR. THE CATHODE, OR BANDED SIDE OF THE DC TRANSORB OR DIODE, CONNECTS TO THE POSITIVE SIDE OF THE POWER SUPPLY. WITHOUT THESE SNUBBERS, COILS PRODUCE VERY LARGE VOLTAGE SPIKES WHEN DE-ENERGIZING THAT CAN CAUSE MALFUNCTION OR DESTRUCTION OF ELECTRONIC CIRCUITS.

ACI recommends 16 to 26 AWG twisted pair wires or shielded cable for all transmitters. ACI recommends using BELDEN 3105 for communication(Modbus) wiring. This wire has 120 ohm input impendence. The terminal blocks allow for (1) or (2) wires to be connected in each position for daisy chaining. Daisy chain the RS-485 wiring and do not use “Star” or “T” wiring.

Avoid running communication wires next to AC line voltage wires. These can be sources of noise that can aflect signal quality.

FIGURE 8: WIRING FIGURE 9: JUMPER SETTINGS

DEVICE CONFIGURATION THROUGH MODBUS RTU

MODBUS RTU INTERFACE
The Modbus Remote Terminal Unit (RTU) data link protocol uses EIA-485 as a two-wire, daisy chain network. A branch is a discrete chain of devices connected to a controller. The max number of devices per segment is (32), as per the Modbus speciflcations. 4000 ft (1219.2 m) is the maximum recommended length for a segment, which includes all devices from the controller to the last device in the daisy chain.

Each branch must have all devices connected with (A) connected to (A) and (B) connected to (B). If a shielded cable is used, this is not to be connected to the devices. The shield cable should only be connected on one end to earth ground, usually at the controller. Each device must be conflgured for the correct baud rate and have a unique address in each branch. The baud rate for the branch is set by the controller.

EOL Termination Resistance Selection
RS-485 requires that the last device in a chain have a termination resistor. This is controlled using the J8 switch as shown in FIGURE 11. When the jumper is set to ON(Enabled), a 120 Ohm resistance is added in parallel to the data line. When the jumper is set to the left(Disabled), the resistance is not added. By default, the jumper is placed in the disabled position.

FIGURE 10: EOL TERMINATION

A typical Modbus RTU mode message frame is shown below. In the Modbus RTU mode, the messages between frames are separated by at least 3.5 characters time’s silent interval. If the silent interval between two characters is more than 3.5 characters time, the former character was transferred successfully, and the current character’s transmission starts

MODBUS MESSAGE

ADDRESS SELECTION
Modbus can locate up to 256 diflerent addresses, including valid addresses from 1-247. Address 0 is for broadcast and address 248~255 are reserved for special addresses. Slave address can be set with compatible Modbus RTU software. Default address is 1.

BAUD RATE, DATABITS, PARITY, AND STOPBITS SELECTION
Baud rate is set to 9600, but can also be conflgured to 4800 via the register. The device that requests information is called the Modbus Master and the devices giving the information are Modbus Slaves. The Modbus sensors are slave devices and the number of Data Bits needs to be the same as in the Master device conflguration. ACI’s Modbus RTU sensors utilize 8 data bits during communication exchange. Parity default setting is NONE. Stopbit default setting is 1. Both settings can be adjusted via the register.

FUNCTION
The function code is the second data in the frame. Valid function codes are from 0~127 (01H~7FH). See the relevant Modbus standard. It supports 03H/06H function codes, shown as the following Modbus Poll software. The detail register addresses are in: 6 General registers table.

BROADCAST MODE TO WRITE DATA TO SLAVE

Using broadcast mode, customer can write data to all slaves connected to the network. Address of broadcast mode to write data is 0.
For example: change slave address with broadcast mode, customer can set a new slave address. Note: since this operation will modify all the addresses of the slavers to the same address, it is NOT applicable for network of more than one slave.

SPECIAL MODE TO READ DATA FROM SLAVE
With the special mode, customer can read the register data under the circumstance of NOT knowing the slave address.

Address of special mode read data: 255(0xFF)
Note: this operation is applicable for ONLY ONE slave in the network.

MODBUS RTU MAP

Register Address	R/W	Type	Definition	Remarks
40001, 00000	R	Signed	Product code	Product code
40002, 00001	R	Signed	Equivalent CO2 value	equivalent CO2 value, Unit: ppm

0x80 error. 0xAA: is not connected.

0xff: Wrong Alarm.

(RTU,9600,8,n,1), Range: 1~255

40015, 00014| R/W| Signed| Reserved|
40016, 00015| R/W| Signed| Function register| Write ( 06 function ) “21485”

to return factory setting

40017, 00016| R/W| Signed| Not Applicable| NA
40018, 00017| R/W| Signed| Not Applicable| NA
40019, 00018| R/W| Signed| Not Applicable| NA
40020, 00019| R/W| Signed| Not Applicable| NA
40021, 00020| R/W| Signed| Not Applicable| NA
……| | | |
40029, 00028| R/W| Signed| Baud rate| 4800 or 9600
40030, 00029| R/W| Signed| Parity| 0: NONE,1: ODD,2: EVEN

Note:

40001 is PLC mode ADDRESS (BASE 1); 00000 is PROTOCOL ADDRESS (BASE 0).
Function register 40016 instructions :
- Use the 06 function code to write 21845 to the register 40016 and return the factory settings.
- Use the 06 function code to write 23278 to the register 40016, and save the parameters.

PRODUCT SPECIFICATIONS

WARRANTY

The ACI VOC Duct Series are covered by ACI’s Two (2) Year Limited Warranty, which is located in the front of ACI’S SENSORS & TRANSMITTERS CATALOG or can be found on ACI’s web site: www.workaci.com.

W.E.E.E. DIRECTIVE
At the end of their useful life the packaging and product should be disposed of via a suitable recycling centre. Do not dispose of with household waste. Do not burn.

Automation Components, Inc.