Johnson Controls METASYS ASC Networking And Troubleshooting Manual
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Johnson Controls METASYS ASC Networking And Troubleshooting Manual

Johnson Controls METASYS ASC Networking And Troubleshooting Manual

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Networking and Troubleshooting Guide
© 1995 Johnson Controls, Inc.
Code No. LIT-6363003
ASC and N2 Bus
* Indicates those sections where changes have occurred since the last printing.
Application Specific Controllers Technical Manual 636.3
Introduction Section
Technical Bulletin
Issue Date 0995
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Summary of Contents for Johnson Controls METASYS ASC

  • Page 1: Table Of Contents

    TEST 3: N2 Bus Polarity, Shorts, Crossed Wires, Grounds TEST 4: Oscilloscope Diagnostic LEDs on the AHU Installing UNTs Used with Gas Ignition Devices * Indicates those sections where changes have occurred since the last printing. © 1995 Johnson Controls, Inc. Code No. LIT-6363003...
  • Page 2 Metasys Installation Practices Page Quiet Wiring vs. Noisy Wiring Using Enclosures for ASCs Hard and Soft Grounding Using Shielded Cable in Noisy Environments Sample Installations with Shielded Cable Suppression Devices Summary of Installation Practices Zone Bus Communications Zone Bus Description Cable Pro Description Cable Connector Description Troubleshooting...

  • Page 3: Introduction

    Introduction This document contains important information on how to install and Overview 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.
  • Page 4 4 Introduction—ASC and N2 Bus Networking and Troubleshooting Guide...

  • Page 5: Installing Asc Controllers

    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.

  • Page 6: Asc Installation Steps

    This section describes how to install ASCs. The ASCs include the Air ASC Installation Handling Unit (AHU) Controller, Lab and Central Plant (LCP) Controller, Steps Unitary (UNT) Controller, and Variable Air Volume (VAV) Controller. Notes: These procedures are not required; however, they are recommended to reduce installation errors.
  • Page 7 3. Before connecting the transformer to the ASC, connect the input power to the primary leads of the 24 VAC transformer. 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;...
  • Page 8 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. VAV/UNT100 24 VAC 15 VDC...
  • Page 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.
  • Page 10 10 Introduction—ASC and N2 Bus Networking and Troubleshooting Guide...

  • Page 11: Installing The N2 Bus

    Installing the N2 Bus The N2 Bus is a “daisy chain” communications line. Essentially, it Background consists of three wires which carry three signals: N2+, N2–, and REF. Information 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.
  • Page 12 “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.
  • Page 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...
  • Page 14 5 VDC 1200 ohm W1=MM-CVT101 W2=Companion Panel/LTD Switch W2=MM-CVT101 PRC=Microprocessor W4=Companion 1200 ohm Panel/LTD EOLWIRE2 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. 5 VDC 100K ohm 18-50K...
  • Page 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):...
  • Page 16 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.
  • Page 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.
  • Page 18 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.
  • Page 19 Important N2 Bus Table 4 lists characteristics of various Companion devices that are Characteristics 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.

  • Page 20: N2 Bus Installation Steps

    This procedure allows you to test for proper voltage and polarity of the N2 Bus following components: Installation Steps 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.
  • Page 21 N2 Bus Terminal Block on LTD Companion MM-CVT101 or Panel/ N2 + N2+ to REF +2.45 to 2.98 VDC N2 - N2- to REF +2.06 to 2.54 VDC N2+ to N2- +0.36 to 0.92 VDC Note: For best reading, place probe on metal VOLTAGE plate inside terminal, not on screw.
  • Page 22 N2 Bus Terminal Block UNT / VAV AHU / LCP N2 - N2 + N2+ to REF +2.45 to 2.98 VDC N2 + N2 - N2- to REF +2.06 to 2.54 VDC N2+ to N2- +0.36 to 0.92 VDC ZBus Note: For best reading, place probe on metal plate inside terminal, not on screw.

  • Page 23: Troubleshooting N2 Bus Installation

    Troubleshooting N2 Bus Installation You need to troubleshoot the N2 Bus if the Companion system is not Overview properly communicating with the ASCs. This section first presents a troubleshooting table. The table covers many ASC or N2 communication problems and suggests which actions to take. Second, specific troubleshooting tests are given.

  • Page 24: Troubleshooting Chart

    Table 5: Troubleshooting Troubleshooting Symptom Possible Cause Action Chart N2 Bus is EOL jumpers and/or W3 jumper on Install EOL jumpers and W3 jumper MM-CVT101 or Companion properly. offline. Panel/ LTD are not installed. MM-CVT101 is not plugged into Plug MM-CVT101 into PC or plug it PC or 120 VAC source.

  • Page 25: Test 1: Earth Grounded 24 Vac Load

    This test applies only to the VAV100/101 and UNT100/101 Controllers TEST 1: Earth only. You’ll need a 100K ohm resistor and a DMM to perform this test. Grounded 24 Follow these steps: VAC Load 1. If you have a Companion PC Version, remove the 25-pin RS-232 connection from the MM-CVT101 converter.

  • Page 26: Test 2: Ground Loop (Isolation)

    b. Repeat Step 3a for the other two N2 Bus wires. At the ASC that you suspect is causing the ground loop, measure its +15 VDC (or +30 VDC) terminal to earth ground using the DMM in parallel with a 100K ohm resistor. If the value is greater than 5 VDC/VAC, disconnect the N2 Bus at the ASC.

  • Page 27: Test 3: N2 Bus Polarity, Shorts, Crossed Wires, Grounds

    You’ll need a DMM to perform this test. By connecting the DMM to each TEST 3: N2 Bus N2 Bus wire, you’ll be able to detect polarity, shorts, crossed wires, and Polarity, Shorts, grounds. Crossed Wires, Grounds Follow these steps, referring to Figure 14: 1.

  • Page 28: Test 4: Oscilloscope

    3. Check the voltage and polarity of the N2 DC bias voltages at the ASC. Do so by connecting the DMM across N2+ and REF (Figure 14). Write down the reading. Repeat for N2– and REF, then for N2+ and N2–. Compare the voltages you read to the following values: N2+ to REF = +2.45 to 2.98 VDC N2–...

  • Page 29: Diagnostic Leds On The Ahu

    6. Connect channel B to the N2– wire and connect channel A to the N2+ wire. (Do not use the oscilloscope ground lead.) 7. Compare the signal you measure with the waveform in Figure 15. They should resemble the figure. A signal outside this range indicates that the N2 Bus is not functioning properly.
  • Page 30 30 Introduction—ASC and N2 Bus Networking and Troubleshooting Guide...

  • Page 31: Installing Unts Used With Gas Ignition Devices

    Installing UNTs Used with Gas Ignition Devices Gas ignition devices for rooftop units require that you use shielded wiring to a UNT Controller. These devices generate very high levels of electrical noise that can interfere with N2 communication. For information about how to install these devices in rooftop units, refer to the UNT Controller Technical Bulletin in this manual.
  • Page 32 32 Introduction—ASC and N2 Bus Networking and Troubleshooting Guide...

  • Page 33: Metasys Installation Practices

    Metasys Installation Practices This document uses the terms “quiet” wiring and “noisy” wiring. With Quiet Wiring vs. wiring gas ignition devices especially, it is important to know the Noisy Wiring difference between the two. Quiet Wiring--Wiring that is free of transients. This wiring includes binary inputs, analog inputs and outputs, 24 VAC power, and communication buses.

  • Page 34: Using Shielded Cable In Noisy Environments

    In most equipment locations, whether or not to provide a low impedance connection to earth ground depends on the circumstances. The high frequency components of electrical noise can render a long wire connection to ground practically useless because of the wire’s inductance. Wherever possible, connecting a shield to a large sheet metal enclosure, such as a rooftop unit, is much better than trying to find a “true”...
  • Page 35 Rules for Using Follow these rules and recommendations when using shielded cable for Shielded Cable the N2 Bus. (Several examples that show these rules in effect follow this section.) Hard ground the shield at the Panel/LTD or PC Version Companion. This is the only location that the N2 shield is hard grounded.

  • Page 36: Sample Installations With Shielded Cable

    The configuration shown in Figure 16 indicates how to use shielded cable Sample between ASCs that are in separate enclosures. Installations with Shielded Cable Enclosure Enclosure MM-CVT101-x or Pane/ LTD Companion N2 Bus N2 Bus 560 pF Ground within 1 inch of enclosure's EXIT.
  • Page 37 The configuration shown in Figure 17 indicates how to use shielded cable between ASCs and devices that are in the same or separate enclosures. Metal Enclosure Companion PC or Panel/ LTD N2 Bus N2 Bus N2 Bus N2 Bus M100C Zone Bus Metal Case Metal Enclosure...
  • Page 38 The configuration shown in Figure 18 indicates how to use shielded cable between ASCs and devices that are in two separate enclosures. Metal Enclosure Companion PC or Panel/ LTD N2 Bus N2 Bus N2 Bus Metal Enclosure N2 Bus Tape back shield Notes: Hard ground (HG) the N2 Bus shield within 1 inch of each enclosure.

  • Page 39: Suppression Devices

    In most installations, reliable controller operation is ensured by a separate Suppression isolation transformer or step-down transformer to provide 24 VAC to a Devices UNT or VAV Controller. However, in environments where transient electrical noise is present on power lines, you must take further precautions to prevent unwanted BO cycling or other possible controller malfunctions.
  • Page 40 Table 7: Recommended Suppression Devices (MOVs) Power Transformer Primary Voltage 120 VAC 208 to 240 VAC 277 VAC 347 VAC Minimum Continuous 130 to 135 VRMS 250 to 280 VRMS 300 to 320 VRMS 385 VRMS Voltage Rating Only 250 V types listed 30 Joules 55 Joules...

  • Page 41: Summary Of Installation Practices

    Follow these installation practices, listed in order of importance: Summary of Installation 1. Use a line filter with gas ignition systems. Practices 2. Use unshielded cable for your N2 Bus application. The only case you need shielded cable is if the bus is routed near “noisy” wire, which is typically from switched line-voltage loads, gas ignition, and line- voltage distribution.
  • Page 42 42 Introduction—ASC and N2 Bus Networking and Troubleshooting Guide...

  • Page 43: Zone Bus Communications

    Zone Bus Communications The Zone Bus is a 2-wire communications bus that allows a computer to Zone Bus communicate with the ASC to download the ASC’s data base and to Description communicate with Zone Terminals and M100s. A third wire is used for 24 VAC power to the Cable Pro, Zone Terminal, and CBLCON.

  • Page 44: Cable Pro Description

    The AS-CBLPRO is an interface device for use between a PC or laptop Cable Pro computer running HVAC PRO software and ASCs. It is used for data Description base downloading, uploading, or commissioning via the Zone Bus communication port. There are three models: the AS-CBLPRO-0 (Figure 19), AS-CBLPRO-1 (also Figure 19), and AS-CBLPRO-2 (Figure 20).
  • Page 45 To Power To LCP (12 VDC) To ASC, Zone Terminal, Metastat To Laptop PC CBLPRO-2 Figure 20: Cable Pro Model AS-CBLPRO-2 AS-CBLPRO-2 The AS-CBLPRO-2 (Figure 20) is an improved model of the original Cable Pro AS-CBLPRO-0, -1. It has the following improvements: The laptop PC cable is permanently attached to the Cable Pro, making PC attachment more convenient.

  • Page 46: Cable Connector Description

    Table 9: Descriptions of Diagnostic LEDs on AS-CBLPRO-2 ZB LED LCP LED Normal And Fault Conditions 2 Flashes/Sec Connected to the Zone Bus--Normal Communication 2 Flashes/Sec Connected to the LCP--Normal Communication 1 Flash/Sec Connected to the Zone Bus--No RS-232 Communication 24 VAC Shorted to Zone Bus 5 Flashes/Sec 5 Flashes/Sec...
  • Page 47 Table 10: CBLCON LEDs Red LED Green LED Cause No power to ASC Zone Bus wire open Zone Bus wire shorted to Common or CBLCON- 0 switch in download position Blinking Normal communications Table 11 lists and describes the errors that may occur while using the Troubleshooting ™...
  • Page 48 An effective troubleshooting technique is to use a CBLCON and watch its LEDs. (Refer to Table 10.) The LEDs will indicate the problem. Another technique is to exchange the component that is believed defective with a working component of the same type. If the error no longer occurs, the component is defective.

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