Johnson Controls METASYS ASC Manuale utente

Application Specific Controllers Technical Manual 636.3

Introduction Section

Technical Bulletin

Issue Date 0995

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)

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

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