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