Johnson Controls VMA1200 Series Service manual

LONWORKS Systems Manual 1162
VMA1200 Section
Issue Date 0501
© 2001 Johnson Controls, Inc. www.johnsoncontrols.com
Code No. LIT-1162350
TECHNICAL BULLETIN
Variable Air Volume Modular Assembly (VMA) 1200 Series
Overview and Engineering Guidelines
VMA1200 Series Overview and Engineering Guide......................... *3
Introduction........................................................................................................*3
Key Concepts.....................................................................................................*4
VMA1200 Series Models...............................................................................................*4
Definition of Terms ........................................................................................................ *6
Theory of Operation.......................................................................................................*9
Establish Zones.............................................................................................................12
Room Sensor Placement...............................................................................................12
Pressure Independent VMA...........................................................................................13
VMA Airflow Rate ........................................................................................................ *13
Power Source.............................................................................................................. *14
LONWORKS Network Topology..................................................................................... *17
Inputs and Outputs...................................................................................................... *19
CablePRO................................................................................................................... *21
CVTPRO..................................................................................................................... *21
Software Tools ............................................................................................................ *21
Related Documentation............................................................................................... *22
Procedure Overview......................................................................................... 23
Detailed Procedures........................................................................................*24
Determining VAV Box Requirements........................................................................... *24
Establishing the Room Schedule...................................................................................25
Developing Bills of Material and Placing Orders............................................................26
Configuring the VMA .....................................................................................................27
*Indicates those sections where changes have occurred since the last printing.

VMA1200
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Appendix A: Reference Information ............................................... *28
Introduction....................................................................................................... 28
VMA Wiring List........................................................................................................... *29
VMA Wiring Interface Diagram.................................................................................... *31
VMA Parts List............................................................................................................. *32
FCC Part 15 Label.........................................................................................................33
VMA Specifications ..................................................................................................... *34
Fabricating Your Own Interconnection Cable............................................................... *38
Sensor Interface.......................................................................................................... *39
Appendix B: Application Example.................................................. *42
Single Duct Application Example.................................................................................*42
*Indicates those sections where changes have occurred since the last printing.

VMA1200 Series Overview and Engineering Guidelines 3
VMA1200 Series Overview and
Engineering Guide
IntroductionThe Variable Air Volume Modular Assembly (VMA) 1200 Series is a
configurable, integrated module that includes a Variable Air Volume
(VAV) controller, actuator, and differential pressure sensor. The VMA
is offered as two models: cooling only and cooling with reheat. The
models, which use the LonTalkprotocol, are designed for pressure
independent, single duct systems. The reheat model can be used with
parallel or series fan powered boxes.
This manual is a reference tool for engineering VMA1200 installations
and applications. It is also a training tool to learn about the
VMA1200 Series controllers. It is task oriented for easy reference to
specific tasks. Refer to the appendixes at the end of this document for
wiring tables and diagrams, a parts list, specifications, and an
application example.
This document describes how to:
•determine VAV box requirements
•establish the room schedule
•develop bills of material and place orders
•configure the VMA

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Key Concepts
VMA1200 Series Models
Table 1 lists VMA1200 Series features. Table 2 shows available
VMA1200 models.
Table 1: Feature Checklist
VMA Features Comments
Applications
Pattern Recognition Adaptive Control (PRAC)
on Zone Proportional Plus Integral (PI)
Temperature Loops
Eliminates manual tuning and seasonal retuning.
Adaptive Flow Control Loops No manual tuning, improved control and energy savings
Single Duct, Pressure Independent VAV Meets most VAV applications.
Side Loops without Interlocking Single Analog Input (AI) to Analog Output (AO)/Binary
Output (BO)
Fan Powered Boxes Series or parallel
Incremental, Proportional, and Three Stages
of Box Heat Up to three stages or normally open/closed valves
Incremental, Proportional Two Position, or
One Stage Supplemental Heat Normally open or closed valves
Damper Actuator
Clockwise (CW)/Counterclockwise (CCW)
Rotation Selection Set via M-Pro software, VMA1200 Balancing Tool (VBT) software, or network management tool for either direction
to close.
Software/Tools
Ability to Download Code Firmware Firmware code is upgradeable without removing the VMA.
Diagnostics
Moving Average Flow/Temperature
Diagnostic Provides standard measure of control loop performance over time.
Actuator Duty Cycle Diagnostic Indicates shaft slippage.
Commissioning
Balancing Tool with Automatic K-factor
Calculation Palmcompatible handheld device (Version 2.0 or later
operating system) on Zone Bus
Hardware
24 VAC Isolation Eliminates 24 to 24 VAC transformer and polarity concerns.
Multiple VMAs Powered by a 100 VA
Transformer Up to 14 cooling only. Number of reheat/fan units depends on power consumption of valve/fan relays.
Isolated Communication, Binary Outputs, and
24 VAC Saves installed cost and improved electrical noise rejection.
Ability to Drive Low Current Relays Down to
25 mA Eliminates relay chatter.
13-Bit Analog Input/8-Bit Analog Output
Resolution High accuracy and good device control
Analog Input Jumpers Eliminated All analog inputs are preset reducing labor.
Continued on next page . . .

VMA1200 Series Overview and Engineering Guidelines 5
VMA Features (Cont.) Comments
Differential Pressure Transducer
Dead Ended Transducer No filters or maintenance required.
Capacitive Technology Improved stability
Industry Accepted Flow Measurement
Accuracy Even for flows below 250 fpm (1.25 m/s) typical
Temperature Sensors
Variety of Sensors Nickel, 1K platinum, 2.25K NTC
Temporary Occupied Button On TMZ1600, TE-6700, TE-7000 (Europe only) Series
room sensors
Temporary Occupied Light-Emitting Diode
(LED) On TMZ1600, TE-6700, TE-7000 (Europe only) Series room sensors for Occupied and Unoccupied modes
LED Indicator for Operation
Power/Communication Verifies operation and power connections.
Physical
Small, One Piece Assembly
102 x 153 x 102 mm (4 x 6 x 4 in.) Prewired to reduce installed cost.
Plenum Plastic Housing Rating UL 94-5VB plenum flammability may eliminate metal box
(check local codes).
Removable Input/Output (I/O) Screw
Terminals Two or three position accessory kits
Node Installation
Service Pin Message Local pushbutton and remote access from Palm compatible
handheld device
Wink Function Initiate via Palm compatible handheld device or network
management tool.
Bar Code Label Two removable bar code labels printed with NeuronID

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Table 2: VMA1200 Series Models
Inputs/Outputs Points Rating VMA1210
(Cooling
Only)
VMA1220
(Cooling
w/Reheat)
Analog Inputs:
Zone Temperature
Zone Setpoint
Humidity, Dewpoint, or Sideloop
Supply Air Temperature or
Supplemental Heat Temperature
Velocity Pressure
AI-1
AI-2
AI-3
AI-4
Internal
1K Ni or Pt or 2.25K NTC
1.6K ohm Potentiometer (Pot.)
0-10 VDC
1K Ni or Pt or 2.25K NTC
0-1.75 inch W.C. (0-436 pa)
✔
✔
✔
✔
✔
✔
✔
✔
Binary Inputs:
Temporary Occupied/
Standby/Room Sensor LED
Occupied
Off or Window or Shutdown
BI-1
BI-2
BI-3
Dry contact
Dry contact
Dry contact
✔
✔
✔
✔
✔
✔
Analog Outputs:
Proportional Heat AO-1 0-10 VDC @ 10 mA ✔
Binary Outputs:
Fan
Box Heat--Incremental Valve or
1-3-stage Electric
Supplemental Heat--Incremental
Valve or 1-3-stage Electric
BO-1 to
BO-5 24 VAC triac @ 0.5A ✔
Actuator Motor Internal ✔✔
Definition of Terms
Auto Calibration
The VMA has an Auto Calibration mode that runs periodically to
adjust the pressure sensor calibration due to offset tolerance and
mounting position.
Binding
A process performed by a network management tool that connects
Network Variable Outputs (NVOs) and Network Variable Inputs
(NVIs). These connections provide for peer-to-peer data transfers.
Commissioning
Verification of controller inputs and outputs and modification of the
controller configuration properties to meet installation specifications.
Configuration Properties
Data stored in non-volatile memory (Flash) in the controller that is
accessible from a network management tool.

VMA1200 Series Overview and Engineering Guidelines 7
Configuring
Building an application within the controller to establish the required
control sequence, setting the functionality of the controller.
Downloading
Writing the Heating, Ventilating, and Air Conditioning (HVAC)
application data and configuration properties to the controller. This is
accomplished using a software tool with a Personal Computer (PC).
LONWORKS 


Network Services (LNS


 ) Protocol
Network management system protocol for LONWORKS devices.
LONWORKS FTT-10A Transceiver
The Free Topology Transceiver (FTT) interface between the
VMA1200 and the physical network.
M-Pro
A software tool used to configure and download controllers.
M-Pro software is part of the System Tools in M-Tool.
Neuron
The microprocessor used in the VMA. Each neuron has a unique
48-bit ID for node identification.
NVI/NVO
LONMARKterm for Network Variable Inputs/Outputs. These
variables may be read/written by network management tools. They
may be bound to other network variables in a system.
Palm Compatible Handheld Device
A handheld computer that uses software to configure and balance the
VMA1200. The PalmPilotunit is an example of this device.
SCPT/UCPT
LONMARK terms for Standard Configuration Property Type and User
Configuration Property Type.
SNVT/UNVT
LONMARK term for Standard/User Network Variable Types.
A SNVT/UNVT defines the units, structure, and resolution of the
configuration properties, NVIs and NVOs.

VMA1200
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Test and Balance (TAB)
Test and Balance (TAB) is a function performed to ensure the installed
system operates to design specifications. Balancing of the VMA zone
indicates whether the VAV terminal box achieves minimum/maximum
airflow settings. TAB must also be performed for the air handler and
the air duct distribution to the VAV box.
Variable Air Volume (VAV) Controller
An Application Specific Controller (ASC) used for digital control of
single duct, dual duct, fan powered, and supply/exhaust VAV box
applications.
Variable Air Volume Modular Assembly (VMA)
Includes a digital controller with integrated pressure transducer and
actuator.
Zone Bus
A local interface between the controller and the room sensor. By
connecting a Palm compatible handheld device with the proper
software to the CablePRO or CVTPROx00-0 and room sensor, the
Zone Bus allows you to monitor and commission directly through the
room sensor.

VMA1200 Series Overview and Engineering Guidelines 9
Theory of Operation
VAV systems are most easily understood by considering them as
cooling applications. As the zone temperature increases due to heat
produced by people, computers, or other heat sources, the VMA opens
the VAV box damper and lets cooler air in. The size of the space and
the internal and external heat loads dictate the volume of air required
to maintain a zone temperature setpoint. In addition, since the size of
the VAV box dictates its maximum cooling capacity, VAV box
performance is dependent upon the design engineer sizing the box for
each zone. If the installed unit is too small, insufficient cooling results,
and excessive flow rates cause audible noise. If the installed unit is too
large, proper control is difficult to maintain, since a small change in
damper position causes excessive airflow change. Boxes are
sometimes oversized to ensure quiet operation or to reserve cooling
capacity as zone usage changes.
A cooling only VAV system maintains a constant zone temperature
while varying the flow of air to the space. This is unlike a constant
volume system that maintains a constant volume of airflow to the
space but varies the temperature of the air stream in response to space
temperature changes. VAV systems are predominantly single duct, but
some are dual duct designs. The VMA can be configured for most
single duct pressure independent VAV applications. The M-Pro
software (part of M-Tool Release 2.0) is used to configure and
download VMA1200 applications.
The actuator drives the damper from full open to full closed in
90 seconds. The VMA incorporates flow feedback to accurately
position the damper and to minimize position hunting and motor
runtime. Control performance metrics are recorded and are available
via network variables to the MetasysOperator Workstation (OWS).
Figure 1 shows the VMA1200 in the Metasys Network. Figure 2 is a
functional block diagram of the VMA1200.

VMA1200
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Operator Workstation
(with OWS, M-Pro,
and LNS Software)
Network Control Module (NCM)
N1 LAN
Room
Sensor
VMA1200
Zone
Bus
FTT-10
Palm Compatible
Handheld Device
MNET
LW
Network
Bus
ON ORKS
CablePRO
Converter
LW
Compatible
Devices
ON ORKS
Room
Sensor
Zone
Bus
Palm Compatible
Handheld Device
CVTPRO
Converter
VMA1200
Figure 1: VMA1200 Controllers in Metasys Network Diagram

VMA1200 Series Overview and Engineering Guidelines 11
Neuron
Application
Processor
FTT-10
Interface
COP8
IO Processor
Fblock2
Digital
Inputs
x3
Analog
Inputs
x5
Phone
Jack
Zone
Bus
Analog
Output
x1
Triac
Outputs
x7
Window Open
Occupancy Sensor
Temp Occ Button
Hi
Low
Space Temperature
Space Setpoint
Auxiliary Temperature
Auxiliary 0-10V
TE-6700, TMZ1600, or
Palm Compatible
Handheld Device
Heating Valve
Five 24 VAC Outputs for
Fan, Staged Heating, etc.
L W Network
ON ORKS
Isolated
CW CCW
Differential
Pressure
(DP) Sensor
Actuator
Motor
Figure 2: VMA1200 Functional Block Diagram

VMA1200
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Establish Zones
When designing VMA systems, establishing zones correctly is critical
to take maximum advantage of the VMA’s exceptional accuracy and
rapid response capabilities.
The designer strives for the most uniform indoor environmental
conditions possible. A single thermostatic device (room sensor)
controls each area. A zone could also be thought of as an area where
the load is considered the same for every square foot of floor space.
HVAC system zones fall into two major categories: exterior zones and
interior zones. Exterior zones are spaces directly affected by outdoor
weather conditions. Heat losses or outdoor air conditions do not
influence interior zones. Interior zones usually have cooling or
ventilation requirements only.
Further divisions of interior/exterior zones may be required to
accommodate different occupancy schedules and/or solar loads.
Variations in internal loading dictate the selection of separate zones.
For example, in a restaurant, the kitchen has vastly different heating
and cooling requirements from the seating area.
Room Sensor Placement
Consider room sensor placement for each zone, making sure to:
•Verify that the room sensor is the correct one for the application.
•Review architectural requirements such as furniture height and
location, aesthetics, and type of mounting. Wall plates are required
if mounting on a conduit handibox.
•Review room sensor location. The best room sensor location is on
an interior wall, about five feet above the floor, out of direct
sunlight, out of the direct path of supply air from the diffuser, away
from heat sources, such as equipment, machines, and perimeter
radiation, and away from doors and other draft sources. Mounting
height may be affected by local codes or the accessibility needs of
persons with disabilities.
•Do not locate a sensor near zone boundaries where primary
influence is from an adjacent zone.

VMA1200 Series Overview and Engineering Guidelines 13
Pressure Independent VMA
The pressure independent VMA employs patented self-tuning,
cascaded proportional/integral control loops. The zone temperature
loop samples space temperature and resets the airflow setpoint
between the minimum and maximum flow settings. Since inlet duct
static pressure influences the amount of air passing through the
VAV box, the VMA airflow loop samples airflow via a flow pickup in
the box inlet. It modulates the damper to control the flow. Thus, the
VAV box flow is independent of duct static pressure.
The engineering basis for this method of control is that the temperature
of a space with a constant load is linearly proportional to the flow of
conditioned air into the space. The engineer must accurately determine
the required maximum and minimum flow for each space based on
heating, cooling, and ventilation loads.
VMA Airflow Rate
The VMA determines airflow rate by dynamic pressure measurement.
The VMA contains a Differential Pressure Transmitter (DPT) to sense
differential pressure in pressure independent VAV applications.
The DPT is connected to the VAV box airflow pickups. It measures
differential pressure and generates a proportional voltage signal. The
voltage signal from the DPT is read by the VMA and converted to
airflow in cubic feet per minute (cfm) or liters per second.
The DPT provides maintenance-free performance within the control
range of 1.25 to 18 m/s (250 to 3500 feet per minute [fpm]) when used
as recommended.
The minimum 1.25 m/s (250 fpm) velocity and the gain of the airflow
pickup produce an accurately measured pressure difference.
The VMA Auto Calibration function helps reduce the temperature
effect error by zeroing offset errors. As the ambient temperature
swings relative to the temperature at which the Auto Calibration
occurred, an offset error may occur (typically ±0.179 Pa/°C
[±0.0004 inch W.C./°F]). When calibration occurs, this error becomes
zero.
The error envelope becomes smaller with increased airflow pickup
gain and with smaller ambient temperature deviations at the
transmitter location.

VMA1200
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Power Source
You can use one 24 VAC power trunk to power multiple VMAs. In
this case, transformers of up to 100 VA are centrally located, and the
secondary run is without conduit and without concern about polarity.
Notes: The 24V power transformer must be UL/CSA listed as
NEC Class 2 Power Limited.
See NEC Article 725/Class 2 (30 VRMS maximum) and
(100 VA maximum).
The VMA1210 draws 7 VA including the internal damper actuator.
Therefore, 14 VMAs can be powered from one 100 VA transformer
without conduit. The number of VMA1220s is dependent on the
binary output loads and reheat actuators. The reheat actuators must be
added to the 7 VA of the controller, then divided into the 100 VA
transformer power. For example, the VMA1220 draws 7 VA without
loads. If there were only a single VA-8020 reheat valve per VMA, its
4 VA must be added to the VMA for a total of 11 VA. Then
nine VMA/VA8020s can be powered from one 100 VA transformer.
Table 3 shows the power rating for several cooling/heating coil valve
actuators. The valve power plus the VMA power must not exceed
100 VA. If a device is not listed in the following table, refer to the
product literature for that device.
Table 3: Actuator VA Power Rating
Actuator Type Power Rating
VA-8020 Incremental 4 VA
VA-8050 Incremental 6 VA
VA-7200 Incremental 6.7 VA
J Series Electric Zone Valve On Off 7 VA
VA-8022 Voltage (0 to 10 VDC) 4 VA
VA-8052 Voltage (0 to 10 VDC) 6 VA
VA-7202 Voltage (0 to 10 VDC) 6.7 VA
VA-7450 Incremental 2.5 VA
VA-7452 Voltage (0 to 10 VDC) 2.5 VA
VA-7050 Thermal (DAO) 3 VA
VA-7310 Incremental 2 VA
VA-7312 Voltage (0 to 10 VDC) 2 VA
VA-7010 On/Off 7 VA
VA-7150 Incremental 2.7 VA
VA-7152 Voltage (0 to 10 VDC) 4.7 VA

VMA1200 Series Overview and Engineering Guidelines 15
When using a single transformer and running 24 VAC to multiple
VMAs, use a wire gauge large enough for the load. The voltage drop
on the 24 VAC cabling is much higher than for line voltage wiring for
the same power draw. For a 100 VA (equivalent to 100 watt) load at
120 VAC, only 0.8 ampere is required. However, at 24 VAC, over
four amperes are needed. Current draw determines the wire size.
Two connection methods are available. In the first method, individual
spade lugs accept a single 10 to 22 American Wire Gauge
(AWG)/4 mm2to 0.8 mm wire and still fit on 6 mm (1/4 inch) tabs. In
the second method, optional screw terminals are assembled over the
spade lugs. The screw terminals accept up to a single 12 AWG
(4 mm2) wire or two 14 AWG (2.5 mm2) wires. When two wires are
crimped into one spade lug, a larger spade lug barrel is needed.
Alternately, a wire nut can connect two heavy wires to a short 152 mm
(6 inch) thinner wire.
24 VAC
100 VA
< 88 ft of 14 AWG >
Example 1:
All VMAs are at one end.
VMA VMA VMA VMA VMA VMA VMA VMA VMA VMA VMA VMA VMA VMA VMA
24 VAC
< 176 ft of 14 AWG >
Example 2:
Transformer is centered.
VMA VMA VMA VMA VMA VMA VMA VMA VMA VMA VMA VMA VMA VMA VMA
100 VA
< 176 ft of 14 AWG >
Cablelength
Figure 3: Power Cable Lengths
A standard 14 AWG (2.5 mm2) wire (top example in Figure 3) is
limited to 27m (88 feet) with 14 cooling only VMAs when the VMAs
are all located at one end of the cable. If the transformer is centered
(bottom example in above figure) with seven VMAs on the left and
seven VMAs on the right, the distance in each direction can be
increased. This is because the current (and voltage drop) are halved in
each direction. In this example, both the left and the right legs can be
increased to 54m (176 feet) from the transformer, creating a 108m
(352 foot) total length.

VMA1200
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Table 4 and Table 5 indicate the relationship between wire length and
power at the end of wires.
Table 4: Maximum Wire Length for Given Power/Gauge (U.S. Measurements)
Wire Size
8 Gauge 10 Gauge 12 Gauge 14 Gauge 16 Gauge 18 Gauge
Power (VA) at
End of Wire Wire Length (Feet)
10 3520 2200 1400 880 550 350
20 1760 1110 700 440 275 175
30 1173 740 467 293 183 117
40 880 555 350 220 138 88
50 704 444 280 176 110 70
60 587 370 233 147 92 58
70 503 317 200 126 79 50
80 440 278 175 110 69 44
90 391 247 156 98 61 39
100 352 222 140 88 55 35
Table 5: Maximum Wire Length for Given Power/
Wire Gauge (Metric Measurements)
Wire Size
4 mm22.5 mm21.5 mm2
Power (VA) at
End of Wire Wire Length (Meters)
10
427 268 168
20
213 134 84
30
142 89 56
40
107 67 42
50
85 54 34
60
71 45 28
70
61 38 24
80
53 34 21
90
48 30 19
100
43 27 17

VMA1200 Series Overview and Engineering Guidelines 17
LONWORKS Network Topology
The LONWORKS FTT-10A used by the VMA1200 supports free
network topologies. Table 6 describes free topologies, and Figures 4
and 5 show supported topologies. For more information, see the
LONWORKS Network Layout Technical Bulletin (LIT-1162150).
Table 6: Free Topologies
Category Free Topology
Architecture Bus, star, ring, or mixed
Termination Single termination for star, ring, or mixed
Double termination for bus
Connection Connected by stub/multi-drop
Free Topology (Tree or Star)
L W Compatible Device
(Including NCM350/361)
ON ORKS
Legend:
Free_Top
Free Topology Terminator
Figure 4: Free Topology

VMA1200
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L W Compatible Device
(Including NCM350/361)
ON ORKS
Bus End-of-Line (EOL) Terminator
Daisy-chained TopologyBus
Stub-wired TopologyBus
Legend:
Bus_Top
Figure 5: Bus Topology
Table 7 contains a specification example for the FTT-10A Transceiver.
This is just one example of the many available wiring styles. For more
complete information, refer to EchelonCorporation
LONWORKS FTT-10A Transceiver User’s Guide.
Table 7: FTT-10A Transceiver Specification Example
Transceiver FTT-10/FTT-10A
Topology Free
Bit Rate 78 kbps
Maximum Node to Node Distance 500m (1640 ft)*
Maximum Total Wire Length 500m (1640 ft)*
Maximum Nodes 64
Node Application Current NA
* Belden 85102, 8471 Cable

VMA1200 Series Overview and Engineering Guidelines 19
Inputs and Outputs
For specific input/output range, wire length, wire size issues, refer to
the VMA Wiring List in Appendix A: Reference Information at the back
of this document.
Note: All terminals are spade lug type except the LONWORKS
Network Bus terminals, which are removable screw terminals.
Optional two or three position kits can be ordered to convert
the spade lugs to removable screw terminals. See Table 12.
Binary Inputs
There are three dry contact binary inputs on the VMA1200. A manual
override button on the room sensor initiates a Temporary Occupancy
mode of operation. The TE-6700 room sensor includes an LED in
series with the button to show the occupancy mode. The switch can be
pushed for as little as 0.2 seconds to detect a change.
The binary inputs on the VMA are inactive when open. They are
active when a contact closure to binary input common (COM) is
applied.
Binary Outputs
The VMA has zero (VMA1210) or five (VMA1220) user accessible
binary outputs. The damper actuator is wired internal to the VMA.
Each load is connected between the BO terminal and BCOM common
terminal. When required to meet codes, the 24 VAC terminal of the
VMA/transformer can be earth grounded. In this situation, the binary
outputs switch the transformer’s low side to the relays and actuators.
Analog Outputs
There is one analog output on the VMA1220. The VMA1210 has no
analog outputs. The load is connected between the analog output and
analog output common (COM) terminals. The output is controlled to
generate a proportional voltage output of 0 to 10 VDC. The maximum
load for each output is 10 mA with a minimum load resistance of
1000 ohms.

VMA1200
20
Analog Inputs
There are two external and one internal analog inputs on the
VMA1210 and four external and one internal analog inputs on the
VMA1220. They are preset for either temperature, setpoint, or voltage.
There are no jumpers to set. Shielding is not required, but if used, earth
ground the shield only at the VMA. You may use 24 AWG (0.6 mm)
twisted pair wire; however, this reduces the allowable wire length due
to the resistance. To minimize sensor error caused by field wiring, the
total resistance of the nickel or platinum resistive sensor wiring should
be less than 3 ohms. The NTC sensor accepts a larger wire resistance.
This wiring error effect is corrected through configuration properties
using a commissioning tool.
Do not share the temperature or setpoint common wire with voltage or
current transmitters on the Zone Bus. The maximum voltage drop on
the common wire must be less than 1 mV.
Zone Bus
The Zone Bus is a 2-wire local communications bus that allows a
Palm compatible handheld device with Johnson Controls VMA1200
Balancing Tool (VBT) software to commission and balance the VMA.
The Zone Bus connector also provides 15 VDC power to the
CablePRO or CVTPRO. The bus sustains no damage in the presence
of fault voltages of 15 VDC or 24 VAC.
Table 8: Zone Bus Specifications
Type
Multi-drop serial communications bus
Speed
1200 baud (bits per second)
Recommended Cable Type
1.5 mm2(18 AWG) with or without shield
(Belden 8760) or
0.6 mm (24 AWG) without shield (unshielded
telephone cable)
Maximum Bus Length
150 meters (500 feet) with 1.5 mm2(18 AWG)
cable or
15 meters (50 feet) with 0.6 mm (24 AWG)
cable
Voltages
Logic High Voltage
Logic Low Voltage
4 VDC minimum (approximately)
1 VDC maximum (approximately)
Data Transmission
1 Start Bit (low level)
8 Data Bits (least significant bit first)
1 Stop Bit (high level)
Isolation
Isolated from 24 VAC, Binary Outputs (BO),
and LONWORKS Network Bus