Johnson Controls METASYS ASC User manual

Application Specific Controllers Technical Manual 636.3
Introduction Section
Technical Bulletin
Issue Date 0995
© 1995 Johnson Controls, Inc. 1
Code No. LIT-6363003
Introduction Page 3
● Overview *3
● Who Should Read This? 3
Installing ASC Controllers 5
● Tools Required 5
● ASC Installation Steps 6
Installing the N2 Bus 11
● Background Information 11
● N2 Bus Installation Steps 20
Troubleshooting N2 Bus Installation 23
● Overview 23
● Troubleshooting Chart 24
● TEST 1: Earth Grounded 24 VAC Load 25
● TEST 2: Ground Loop (Isolation) 26
● TEST 3: N2 Bus Polarity, Shorts, Crossed Wires, Grounds 27
● TEST 4: Oscilloscope 28
● Diagnostic LEDs on the AHU 29
Installing UNTs Used with Gas Ignition Devices 31
ASC and N2 Bus
Networking and Troubleshooting Guide
* Indicates those sections where changes have occurred since the last printing.

2 Introduction—ASC and N2 Bus Networking and Troubleshooting Guide
Metasys Installation Practices Page 33
● Quiet Wiring vs. Noisy Wiring 33
● Using Enclosures for ASCs 33
● Hard and Soft Grounding 33
● Using Shielded Cable in Noisy Environments 34
● Sample Installations with Shielded Cable 36
● Suppression Devices 39
● Summary of Installation Practices 41
Zone Bus Communications 43
● Zone Bus Description 43
● Cable Pro Description 44
● Cable Connector Description 46
● Troubleshooting *47
* Indicates those sections where changes have occurred since the last printing.

Introduction—ASC and N2 Bus Networking and Troubleshooting Guide 3
Introduction
This document contains important information on how to install and
troubleshoot Application Specific Controllers (ASCs) and the N2 Bus on a
CompanionPC, Panel or LTD system. As our experience with this
system matures, we have discovered certain new installation and
troubleshooting techniques, which are described in this document. Please
use this in addition to the ASC and N2 Bus technical bulletins when
installing, commissioning, and troubleshooting ASCs or the N2 Bus.
In particular, this document contains the following sections:
●Installing ASC Controllers
●Installing the N2 Bus
●Troubleshooting N2 Bus Installation
●Installing UNTs Used with Gas Ignition Devices
●MetasysInstallation Practices
●Zone Bus Communications
If you are new to installing, commissioning, and troubleshooting
Metasys products, it is best to read and use this document in its entirety.
However, if you are experienced with Metasys, you probably can just skim
this document.
Note: To provide the greatest assurance that the ASCs will communicate
after initial installation, perform the earth ground test (Figure 4)
and the N2 Bus polarity test (Figures 10 and 11).
Overview
Who Should
Read This?

4 Introduction—ASC and N2 Bus Networking and Troubleshooting Guide

Introduction—ASC and N2 Bus Networking and Troubleshooting Guide 5
Installing ASC Controllers
This section explains how to install ASCs. The VAV and UNT100/101
inputs, outputs, and N2 Bus connections require complete isolation from
earth ground.
!
WARNING: Do not earth ground the 24 VAC high side of the
ASC’s transformer or any of the ASC’s “BO”
terminals. If you do, you will damage all of the
interface components that are connected, including
the Cable Pro, laptop PC, Companion PC, and
MM-CVT101.
In some cases, earth grounding the common side of the AHUs, LCPs, or
UNT110/111s is allowed, because only one earth ground can exist per
ASC. Use these procedures to ensure proper isolation. Test the:
●field device wiring for proper isolation
●transformer for isolation and correct polarity termination
●connected field devices, transformer, and ASC for proper isolation
●transformer and ASC for proper VA load requirements
Obtain the following tools to perform the installation:
●Digital Multimeter (DMM)
●100K ohm resistor, 1/4-watt
●Double banana plug (optional; shown in Figure 1; available from local
electronics store or ITT Pomona Stock No. 34F856 or 34F845)
100K ohm, 1/4-watt
BANANA
Use double banana plug for all tests that require
a 100K ohm resistor placed in parallel with DMM.
Steps:
1. Connect 100K ohm resistor under plug's prongs.
2. Insert banana plug into DMM.
3. Connect leads of DMM into banana plug.
Figure 1: Double Banana Plug Used with 100K Ohm Resistor
Tools Required

6 Introduction—ASC and N2 Bus Networking and Troubleshooting Guide
This section describes how to install ASCs. The ASCs include the Air
Handling Unit (AHU) Controller, Lab and Central Plant (LCP) Controller,
Unitary (UNT) Controller, and Variable Air Volume (VAV) Controller.
Notes: These procedures are not required; however, they are
recommended to reduce installation errors.
If you are fairly confident that the field wiring has no earth
grounds, you may skip Step 2, which instructs you to measure each
field wire terminated to the ASC. Skipping this step shortens the
procedure. If you skip Step 2 and a field device is earth grounded,
it will be caught in Step 5 when the entire ASC is tested.
1. Mount the ASC in an appropriate location as described in its technical
bulletin.
2. Before terminating the field wires to the ASC, measure the resistance
of each wire to earth ground using an LED test circuit (preferred) or a
DMM. For the LED test circuit, assemble the test circuit shown in
Figure 2. Then, connect the circuit from each input to earth ground
and then to each output to ground. For the DMM test, connect the
DMM from each input to earth ground and then to each output to
ground (Figure 2).
If the LED turns On (or you read a value less than 1 Megohm at any
input or output), the circuit is improperly isolated. Replace or repair
the wiring or the field device; or, for a binary output, add an isolation
relay. Repeat the DMM test.
If the LED does not turn On (or you read a value greater than
1 Megohm), the circuit may be properly isolated. (It will not be
isolated if there are earth grounds that exist at higher voltages.)
A value of infinite ohms indicates a completely isolated circuit at
approximately zero volts. Connect this wire to the appropriate ASC
terminal and check the next wire.
Figure 2: Testing for an Isolated Circuit
ASC Installation
Steps
Field Device
IN/OUT
IN/OUT COM
DMM
ISOCIRCT
470 ohm
1/4-watt
9 V
Battery
(+) (-)
Red LED
(15/20 mA)
LED Test Circuit (Preferred Method)
or

Introduction—ASC and N2 Bus Networking and Troubleshooting Guide 7
3. Before connecting the transformer to the ASC, connect the input
power to the primary leads of the 24 VAC transformer.
a. Measure the voltage of each secondary transformer lead to earth
ground with the DMM in parallel with a 100K ohm 1/4-watt
resistor (Figure 3; if using double banana plug, insert plug into
DMM).
If you read 5 VDC/VAC or greater, the transformer is earth
grounded. If this is a VAV or UNT100/101, you’ll need an
isolation transformer in order to isolate the connections from earth
ground and protect system components. Wire a separate 24 VAC
to 24 VAC isolation transformer (such as the Y65) to the ASC. If
this is any other ASC, make sure the ground is on the common side
of the transformer, not on the 24 VAC side.
If you read less than 5 VDC/VAC, the circuit is properly isolated.
Usually a value less than 0.10 VDC/VAC indicates a completely
isolated circuit.
Line
Voltage 24 VAC
TRANSFM1
100K ohm
1/4-watt DMM 100K ohm
1/4-watt DMM
Figure 3: Testing the Transformer
b. Determine the polarity of the transformer’s leads by using a DMM
referenced to earth ground without the 100K ohm resistor.
Connect the transformer’s secondary lead with the higher voltage
potential to the 24 VAC terminal on the ASC. Connect the
transformer’s secondary lead with the lower potential to the
24 VAC Common terminal on the ASC.
4. If the field wires are not yet connected (because you skipped Step 2),
disconnect one 24 VAC wire (or turn off AC power) and terminate the
field wires. Reconnect power.

8 Introduction—ASC and N2 Bus Networking and Troubleshooting Guide
5. Connect the leads of the DMM in parallel with the 100K ohm resistor
from the DC power supply (+15 or +30 VDC) output terminal of the
ASC to earth ground (Figure 4). This tests whether the field devices,
the ASC, and the transformer “assembly” are properly isolated.
Figure 4: Testing for Ground Loops
If you read 5 VDC/VAC or greater, the circuit is improperly
isolated. Follow these steps:
a. Remove all the field wires and N2 Bus wires from the ASC, but
leave the transformer wires attached. With the DMM still
connected, reconnect each set of field wires one at a time until you
read 5 VDC/VAC or greater. At this point, you have discovered
one cause of the ground loop. Correct the problem.
b. Continue to reconnect each set of field wires until all ground loops
are found and corrected. You’ll know that all grounds are
corrected when you read less than 5 VDC/VAC on the DMM.
c. However, if you check all the field wires and you still read greater
than 5 VDC/VAC, the transformer secondary is earth grounded. In
this case, wire a 24 VAC to 24 VAC isolation transformer to the
ASC and measure again. If the value is still 5 VDC/VAC or
greater, replace the ASC.
Note: Binary outputs are often the culprits of ground loops. Therefore,
we recommend that you test the binary outputs of the ASC before
testing other points. Remember, a single earth ground is allowed
on the common terminal of the LCP, AHU, and UNT110/111
Controllers, not on the 24 VAC terminal.
If you read a value less than 5 VDC/VAC, the circuit is properly
isolated. A value of less than 0.10 VDC/VAC indicates a completely
isolated circuit.
Line
Voltage 24 VAC
VAV/UNT100
24 VAC
24 VAC COM
GRDLOOP
DMM < 5 VDC/VAC = OK (Isolated)
DMM > 5 VDC/VAC =
100K ohm
1/4-watt DMM
Field Wiring*
*AICOM, BICOM, ZBUS COM, AOCOM, BOCOM
15 VDC
(30 VDC on AHU)
Earth Grounded

Introduction—ASC and N2 Bus Networking and Troubleshooting Guide 9
6. Connect the DMM across the 24 VAC and the 24 VAC Common
terminal of the ASC. Read the voltage with all typical loads
energized.
A reading of 24-26 VAC is required when the line voltage is nominal.
If you read a value less than 22 VAC, make sure the primary voltage
matches the transformer’s voltage rating. For details, refer to the
appropriate ASC technical bulletin and recalculate the VA
requirements for the ASC.
You have now completed ASC installation. If this ASC is to operate in
standalone mode, you are done with this document. If the ASC is to be
connected to the N2 Bus for communication to other devices, go to the
next section, Installing the N2 Bus.

10 Introduction—ASC and N2 Bus Networking and Troubleshooting Guide

Introduction—ASC and N2 Bus Networking and Troubleshooting Guide 11
Installing the N2 Bus
The N2 Bus is a “daisy chain” communications line. Essentially, it
consists of three wires which carry three signals: N2+, N2–, and REF.
The N2+ and N2– lines carry the actual data signals. The REF line
provides a common reference so that each connected device is capable of
electrically receiving and transmitting data by creating a common voltage
reference among all the devices connected together by the N2 Bus. Three
lines are required. It is important that the N2+ and N2– lines are twisted
together, which allows most induced noise (common-mode noise) from
external sources to affect both lines equally, thereby canceling the noise.
In most installations, the N2 Bus works fine with unshielded cable.
However, in noisy environments, such as near gas ignition devices and arc
welders, shielded twisted wire must be used. Otherwise, the noise disrupts
N2 communications and the ASCs. For more details, refer to the section
Metasys Installation Practices.
An important feature of the N2 Bus is opto-isolation. Isolation prevents
interruption of all N2 Bus communication if any of the controllers on the
bus become grounded. Table 1 below outlines which controllers have
opto-isolation in their N2 Bus circuitry.
Table 1: Opto-Isolated Devices
Controller or Device Opto-Isolation?
AHU Yes
LCP Yes
MM-CVT101 No
UNT100/101 No
UNT110/111/120/121 Yes
VAV100/101 No
The Reference (REF) line helps to provide a common reference from
which each device connected to the N2 Bus can discern the voltage levels,
and hence, the data, on the N2+ and N2– lines. The N2 Bus may connect
devices that are far apart, such as in two different buildings, by allowing
line lengths of up to 15,000 feet with two repeaters. If the N2 Bus is wired
between buildings, a surge protection module should be used at both ends.
Realize that connecting the earth ground of one building to the earth
ground in another building can cause current to flow in the line that
connects the two grounds together. Because of this, the EIA Standard
RS-485 (the N2 Bus) specification states:
Background
Information
N2 Reference
Lines

12 Introduction—ASC and N2 Bus Networking and Troubleshooting Guide
“Where circuit reference is provided by a third conductor, the
connection between circuit common and the third conductor must
contain some resistance (e.g. 100 ohms) to limit circulating
currents when other ground connections are provided for safety.”
For the Companion system, the 100 ohm resistor is located in the RS232-
to-N2 Bus converter (MM-CVT101-0) or in the Companion Panel/LTD.
With N2 Bus grounding in mind, there are a few important facts to know:
●If earth grounded, the UNT-100/101 units and all VAVs may
experience communication problems. This is because the REF line in
these units is connected internally to digital common. The
UNT-100/101s and all VAV controllers are not designed to be earth
grounded, although they often become grounded because field wires
connect to earth-grounded field devices, and thus bring ground into
the digital common of the device. During installation and
commissioning, ensure that no UNT-100/101s or VAVs are earth
grounded. (This does not apply to the newer models that isolate the
N2 from digital common, including: UNT110/111/120/121, all AHU,
and all LCP models.)
●According to RS-485 specifications, the REF protection on most
devices is a 100 ohm resistor. If you miswire the MM-CVT101 or
Companion Panel/LTD by connecting any voltage greater than
5 VAC, you may damage the 100 ohm resistor. The resistor is not
field serviceable, so if the REF line becomes damaged, you’ll need to
send the unit back for repair or replacement.
Most N2 devices have isolated N2 communications power supplies, and
therefore there is no direct path to earth ground through any of the N2
lines. However, there are three exceptions in which an unwanted earth
ground may be introduced into the system:
●From the MM-CVT101, which is not isolated. It is grounded through
pin 7 of the RS-232 connector. Earth ground often comes in from the
ground pin on the PC’s power cord or via a printer connected to the
computer, which in turn connects to the MM-CVT101. The
Companion PC itself is grounded.
●From a surge protection module (i.e., APT Transient Eliminator) on
the N2 Bus. It produces a small amount of leakage to earth ground.
●From the Cable Pro (CBLPRO-0 or -1 only). If the laptop PC is earth
grounded, the Cable Pro would be grounded through the RS-232
ground pin.
A single ground will not cause communication problems unless another
earth ground path exists in the system to complete a ground loop.
N2 Bus
Grounding
Avoiding
Unwanted Earth
Grounds

Introduction—ASC and N2 Bus Networking and Troubleshooting Guide 13
The ASCs have electrical protection built into the N2 Bus transceiver
circuit. It prevents the N2 Bus circuitry from being damaged if someone
inadvertently connects a voltage source greater than 5 VDC/VAC between
any two or the three N2 Bus terminals. Refer to Table 2.
Table 2: Voltage Protection on ASCs
Controller Voltage N2 Bus Circuitry Can Withstand
AHU < 30 VDC/VAC
LCP < 6 VDC/VAC (before 3/1/92)
< 12 VDC/VAC (after 3/1/92)
MM-CVT101-0 < 30 VDC/VAC
UNT < 30 VDC/VAC
VAV < 30 VDC/VAC
The following table summarizes the rules and maximums allowed for
installing the N2 Bus. You may wish to photocopy this table and keep it
handy.
Table 3: N2 Bus Rules
Category Rules/Maximums Allowed
General Only one PC/Panel/
LTD
Version Companion per
N2 Bus
Only daisy-chained devices
Maximum Number of Devices 100 devices per PC/Panel/
LTD
Version Companion
50 devices per repeater
2 repeaters cascaded
Line Length and Type 5000 feet between repeaters
15,000 feet from PC or Panel/
LTD
to farthestASC
(3 segments of 5000 feet each)
26 AWG twisted pair minimum
(stranded 22 AWG or heavier recommended)
Terminations 2 switched EOL per segment (preferred)
1 switched EOL per segment (required)
The N2 Bus uses End-of-Line (EOL) terminations through the use of
jumpers on the Companion Panel/LTD, RS232-to-N2 Bus converter
(MM-CVT101), and repeater. N2 Bus circuitry in the ASCs is self-
terminating. Figure 5 shows an electrical drawing of the end-of-line
wiring for the MM-CVT10-1 and the Panel/LTD Companion.
N2 Bus Rules
N2 EOL
Termination

14 Introduction—ASC and N2 Bus Networking and Troubleshooting Guide
__
N2+
N2-
REF
IN OUT
P
R
C
5 VDC
1200 ohm
220
ohm
1200 ohm
++
EOLWIRE2
EOL
Switch
W1=MM-CVT101
W2=Companion Panel/LTD
W2=MM-CVT101
W4=Companion
Panel/LTD
PRC=Microprocessor
ASC
Figure 5: End-of-line Wiring for MM-CVT101 and
Panel/
LTD
Companion
Figure 6 shows an electrical drawing of the end-of-line wiring for the
AHU, VAV, UNT, and LCP controllers.
__
N2+
N2-
REF
IN OUT
P
R
C
5 VDC
100K ohm
18-50K
ohm
100K ohm
++
EOLWIRE1
PRC = Microprocessor
ASC
Figure 6: End-of-line Wiring for AHU, VAV, UNT,
and LCP Controllers
The EOL terminations on the MM-CVT101 and Panel/LTD Companion
place a:
●direct current “bias” on the N2 wires
●220 ohm resistor from the N2+ to the N2– lines to terminate them
The bias prevents the lines from “floating.” If no communications were
taking place and all the EOL jumpers were set to the Out position, the N2+
and N2– lines would “float.” That is to say, the bus would have no
definite voltage or signal. The receivers would interpret the floating N2
signal as “data,” albeit bad data. To avoid this, and to provide some
impedance termination, one or two end-of-line terminations must be made
on each N2 Bus segment.

Introduction—ASC and N2 Bus Networking and Troubleshooting Guide 15
With the EOL jumpers set to the In position, a positive bias voltage is
applied across the N2+ and N2– lines. This bias voltage is referenced to
the REF line. The bias resistors and the 220 ohm termination resistors
combine to form a voltage divider. By taking the tolerances on the
resistors and the power supply variations into account, you should expect
to see the following voltage levels on the N2 lines (MM-CVT101 is
disconnected from the PC but still connected to the N2 Bus):
Voltage from N2+ to N2– = +0.36 to 0.92 VDC*
(DMM+ probe on N2+ terminal; DMM- probe on N2– terminal.)
Voltage from N2+ to REF = +2.45 to 2.98 VDC
(DMM+ probe on N2+ terminal; DMM- probe on REF terminal.)
Voltage from N2– to REF = +2.06 to 2.54 VDC
(DMM+ probe on N2– terminal; DMM- probe on REF terminal.)
*If the difference from N2+ to N2– is greater than 0.36 V, your system
should be able to communicate.
If communication is taking place, voltage on the N2 Bus fluctuates and
therefore the DMM will read these fluctuating voltages. An oscilloscope
provides a more accurate reading.
Setting the EOL terminations correctly on the devices connected to the
N2 Bus is crucial to proper and reliable communication. Follow these rules:
1. Always set the EOL jumpers to In for the Companion PC or
Panel/LTD. This device is always set as end-of-line because all the
controllers on the N2, namely the ASCs, are self-terminating (they do
not have EOL jumpers). Note that, as in Figure 8, the Companion PC
or Panel/LTD does not necessarily have to be at the end of line.
2. If possible, terminate the two devices that are at the far ends of the
N2 Bus. If one of these devices is self-terminating, terminate the
other, which will have an end-of-line jumper. In many cases, this will
be the MM-CVT101, Companion Panel/LTD, or repeater.
3. If only one device on the bus can be terminated, jumper it as an
end-of-line device.
During commissioning, visually check the N2 EOL jumpers at the
Companion PC or Panel/LTD.
●For the Panel/LTD version, the end-of-line jumpers are located on the
Panel’s circuit board (W2 and W4).
●For the PC version, the jumpers are located on the MM-CVT101
(W1 and W2).
●For the repeater, the jumpers are found under the top cover.
Proper EOL
Settings

16 Introduction—ASC and N2 Bus Networking and Troubleshooting Guide
To illustrate different possible EOL terminations, consider the following
examples in Figures 7 through 9.
Example One (Figure 7)
In this example, the N2 Bus begins at the PC/Panel/LTD Companion and
connects several ASCs. This is the simplest network and requires only
that the PC/Panel/LTD is set as the end-of-line device.
MM-CVT101
Converter = EOL In
Companion PC Version
Self Termination Self Termination
EOLS1
Self Termination
ASC
Companion Panel/
LTD
Version
Panel EOL = In
or
N2 Bus
ASC ASC
Figure 7: Example One: Companion PC/Panel/
LTD
Terminated

Introduction—ASC and N2 Bus Networking and Troubleshooting Guide 17
Example Two (Figure 8)
In Figure 8, the N2 Bus has a row of ASCs. If the Companion PC or
Panel/LTD is somewhere in the middle of the N2, it would have its EOL
jumpers set to the In position, even though this device is not physically at
the end-of-line. This is because at least one jumpered EOL is needed per
bus.
Figure 8: Example Two: Companion PC/Panel/
LTD
Terminated
ASC ASC
Self Termination
ASC
Self Termination Self Termination
EOLS2
Self Termination
ASC
Self Termination
ASC
MM-CVT101
Converter = EOL In
Companion PC Version
Panel EOL = In
or
N2 Bus
Companion Panel/
LTD
Version

18 Introduction—ASC and N2 Bus Networking and Troubleshooting Guide
Example Three (Figure 9)
In the third example (Figure 9), a repeater is placed near the middle of the
N2 Bus. Side A of the repeater has its EOL set to Out, but side B has its
EOL set to In, since its segment needs a jumpered EOL. Also, the
Companion PC or Panel/LTD has its EOL jumpers set to In.
Figure 9: Example Three: Repeater Used on N2 Bus
ASC ASC ASC
ASC
ASC ASC
A:EOL=Out B:EOL=In
Repeater
A B
Self
Termination Self Termination Self Termination Self Termination Self Termination
Self
Termination
EOLS3
MM-CVT101
Converter = EOL In
Companion PC Version
Panel EOL = In
or
N2 Bus
Companion Panel/
LTD
Version

Introduction—ASC and N2 Bus Networking and Troubleshooting Guide 19
Table 4 lists characteristics of various Companion devices that are
important to installing and commissioning these devices. Note that some
devices do not have EOL jumpers, but have the bias voltage permanently
applied to the N2+ and N2– lines. Other devices may or may not have
isolation of the REF line to the device’s ground. Isolation problems with
communication could possibly result, depending on the situation in which
the N2 lines are used. Refer to the Troubleshooting N2 Bus Installation
section of this document for more details.
Table 4: N2 Bus Characteristics for Various Companion Devices
Device
Type Isolated N2? N2 REF Connection N2± Protection Bias Value EOL Type
AHU Y Transformer isolated from digital
common and earth ground Transient voltage suppressors and PTC1on
unit
100K ohm Self
Termination
CPN201 Y 100 ohm resistor to isolated
transformer common Transient voltage suppressors and PTC on
unit
1.2K ohm Jumper
LCP2Y Transformer isolated from digital
common and earth ground Transient voltage suppressors 2100K ohm Self
Termination2
MM-CVT1013N3100 ohm resistor to common3Transient voltage
suppressors and PTC on
unit
1.2K ohm Jumper
N2 Repeater Y Transformer isolated from digital
common and earth ground Transient voltage suppressors 1.2K ohm Jumper
UNT100/1014N4Tied to digital common Transient voltage
suppressors and PTC on
unit
100K ohm Self
Termination
UNT110/111/
120/1215Y5Transformer isolated from digital
common and earth ground Transient voltage suppressors and PTC on
unit
100K ohm Self
Termination
VAV100/1014N4Tied to digital common Transient voltage
suppressors and PTC on
unit
100K ohm Self
Termination
Notes:
1PTC=positive temperature coefficient thermistor; i.e., a temperature sensitive resistor that acts like a resettable fuse.
2LCPs manufactured before 1/91 should not be used at the end-of-line. LCPs manufactured after 2/92 have transient
voltage suppressors for N2+ and N2– protection.
3MM-CVT101 REF terminal connects to communications ground and earth ground through the PC.
4The UNT100/101 and VAV100/101 have N2 REF connected to digital common. Digital common or 24 VAC must
never be connected to earth ground.
5The UNT110/111/120/121 have isolated N2 REF.
Important N2 Bus
Characteristics

20 Introduction—ASC and N2 Bus Networking and Troubleshooting Guide
This procedure allows you to test for proper voltage and polarity of the
following components:
●RS232-to-N2 Bus converter (MM-CVT101) [Steps 1 and 2]
●Companion Panel/LTD’s RS-485 N2 Bus converter [Steps 1 and 2]
●ASC N2 Bus [Step 3]
●N2 Bus wiring [Step 4]
Follow the steps specific to your installation.
1. If you have a Companion PC Version, remove the 25-pin RS-232
connection from the MM-CVT101 converter. This removes the
fluctuating voltage due to communications and allows you to read the
DC bias voltage. Disconnect the N2 Bus wires. Wire the transformer
to the MM-CVT101 and plug into a 120 VAC source.
If you have a Companion Panel/LTD Version, disconnect the N2 Bus
wires from the Panel/LTD. Wire 24 VAC to the Panel/LTD.
2. Connect the DMM (without a 100K ohm resistor installed) across the
N2+ and REF inputs on the N2 terminal block (Figure 10). Write
down the DC voltage reading. Repeat for N2– and REF, then for
N2+ and N2–. Compare the voltages you read on the DMM to the
following values:
N2+ to REF = +2.45 to 2.98 VDC
N2– to REF = +2.06 to 2.54 VDC
N2+ to N2– = +0.36 to 0.92 VDC
If your readings are not approximately within the ranges listed above,
the N2 EOL device jumpers are probably set incorrectly. For the
PC Version, ensure that pins 1 and 2 on both W1 and W2 of the
MM-CVT101 are jumpered (EOL=In). For the Panel/LTD Version,
pins 1 and 2 on both W2 and W4 of the Panel/LTD circuit board must
be jumpered (EOL=In). If not, jumper them and repeat the DMM
readings. If the voltages read are still not close to those above, and,
after connecting the ASCs to the N2 Bus, the ASCs are still not
communicating, replace the MM-CVT101 or Companion Panel/LTD.
If your readings are approximately within the ranges listed above, the
N2 EOL device jumpers are set correctly. Go on to Step 3.
N2 Bus
Installation
Steps