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Introduction—ASC and N2 Bus Networking and Troubleshooting Guide 23

Troubleshooting N2 Bus
Installation

You need to troubleshoot the N2 Bus if the Companion system is not
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. Before trying one of
these tests, you may be able to determine the cause of the problem by
asking yourself the following questions:

●

Are the N2 Bus wires securely terminated to each ASC?

●

Is the N2 polarity correct?

●

Is the ASC powered and ready to respond?

●

Are the end-of-line device settings correct?

●

Have you cycled power on an ASC after changing its address?

●

Is the W3 loopback jumper on the Companion Panel/LTD fully
pushed down on pins 1 and 2?

●

Are the ASCs configured properly with the correct number of points?

The tests are designed to find opens, shorts, ground loops, or crossed wires
on the N2. Third, this section describes the diagnostic LEDs on the AHU.

!

CAUTION: To avoid electrical shocks when troubleshooting,

always measure the REF to earth ground voltage with
a 100K ohm resistor installed at the DMM. If line-
voltage is measured, have a qualified electrician
locate the fault.

The tests covered in this section require the use of these components:

●

Digital Multimeter (DMM)

●

100K ohm resistor

●

9-volt battery

●

red LED test light

●

470 ohm resistor

●

oscilloscope

Overview

Tools Required

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Содержание METASYS ASC

Страница 1: ...he 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...

Страница 2: ...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 ...

Страница 3: ...oubleshooting 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...

Страница 4: ...4 Introduction ASC and N2 Bus Networking and Troubleshooting Guide ...

Страница 5: ...C 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 ...

Страница 6: ...est 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 impr...

Страница 7: ...he 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 t...

Страница 8: ...ound 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 outpu...

Страница 9: ...nal 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 t...

Страница 10: ...10 Introduction ASC and N2 Bus Networking and Troubleshooting Guide ...

Страница 11: ...s 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 N...

Страница 12: ...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 N...

Страница 13: ...andy 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 farthest ASC 3 segments of 5000 feet each 26 AWG twis...

Страница 14: ... 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...

Страница 15: ...e 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 terminatin...

Страница 16: ...xample 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 Termi...

Страница 17: ...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 Compani...

Страница 18: ...s 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 N...

Страница 19: ...ground Transient voltage suppressors 2 100K ohm Self Termination2 MM CVT1013 N3 100 ohm resistor to common3 Transient 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 1014 N4 Tied to digital common Transient voltage suppressors and PTC on unit 100K ohm Self Termination UN...

Страница 20: ...sistor 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...

Страница 21: ...1991 go on to Step 4 For LCPs manufactured after January 1991 and all other ASCs continue with this step Before connecting the N2 Bus check the voltage and polarity of the N2 DC bias voltages on the ASCs Do so by connecting the DMM across N2 and REF Figure 11 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...

Страница 22: ...entify the correct voltage and polarity of each wire with the DMM The voltages should match the following N2 to REF 2 45 to 2 98 VDC referenced to REF N2 to REF 2 06 to 2 54 VDC referenced to REF REF 1 0 VDC VAC referenced to earth ground with 100K ohm resistor If the voltages are not within the above ranges end of line termination may not be set correctly Locate and fix the problem 5 Connect the ...

Страница 23: ...dy to respond Are the end of line device settings correct Have you cycled power on an ASC after changing its address Is the W3 loopback jumper on the Companion Panel LTD fully pushed down on pins 1 and 2 Are the ASCs configured properly with the correct number of points The tests are designed to find opens shorts ground loops or crossed wires on the N2 Third this section describes the diagnostic L...

Страница 24: ...ed point i e not listed in HVACPRO SYM file Delete the use of the unconfigured point in the Companion process Two or more ASCs have the same address Change each duplicate ASC address to a unique number AO and BO points on the UNT 111 are not communicating The UNT111 was downloaded as a UNT110 Re download the UNT this time specifying it as a UNT111 UNT is offline Points BO 9 and BO 10 are defined i...

Страница 25: ... suspect which ASC is causing the ground loop follow Step 3c on the next page a Connect one DMM lead to REF N2 or N2 and the other to earth ground Figure 12 Read the VDC VAC scale on the DMM If the value is greater than 1 VDC VAC a ground loop is present and therefore the N2 Bus is not properly isolated Subdivide the N2 Bus and measure again Continue to subdivide the bus until you locate the sourc...

Страница 26: ...this test you ll need a red LED test light a 470 ohm resistor and a 9 volt battery Follow these steps referring to Figure 13 1 Disconnect the N2 Bus wires from the Companion PC or Panel LTD 2 Assemble the test circuit as shown in Figure 13 or purchase one with a power supply of 9 volts or greater 3 Connect the ground lead of the battery to earth ground 4 Connect the positive lead from the test lig...

Страница 27: ... screws on the N2 terminal block Figure 14 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 that particular wire is grounded shorted or crossed with another wi...

Страница 28: ...u can use an oscilloscope to pinpoint communication faults over the N2 Bus The procedure requires a 2 channel scope with an A minus B function or an A plus B with B inverted function Follow these steps 1 Plug the scope into a grounded electrical outlet 2 Set both channels to 2 volts per division Both channels must have the same gain or volts per division setting 3 With no signal applied adjust eac...

Страница 29: ...g has T or Y connections installed Check all wiring and devices to pinpoint the problem Replace parts if necessary The AHU102 0 has two diagnostic LEDs that indicate whether the controller is communicating over the N2 Bus and Zone Bus During normal operation the two LEDs are used as Table 6 shows Table 6 Diagnostic LEDs on AHU102 0 Controller Top LED N2 Bus Single blink The AHU is receiving but ha...

Страница 30: ...30 Introduction ASC and N2 Bus Networking and Troubleshooting Guide ...

Страница 31: ...gnition 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 ...

Страница 32: ...32 Introduction ASC and N2 Bus Networking and Troubleshooting Guide ...

Страница 33: ...ded Placing ASCs inside another piece of equipment which contains a metal housing e g a rooftop unit or a motor control center does not constitute locating the control device inside a quiet metal enclosure While the location may provide physical protection for the control device the presence of electrical noise makes it a noisy box Therefore always use a separate grounded metal enclosure for noisy...

Страница 34: ...ribution box 5 Bond to nearby metal water pipe preferably copper Note In all cases make the bond to ground as short as possible Derate a ground point by one level in order of preference for each 50 feet of conductor run between the ground point and the equipment to be grounded For example a water pipe bond located 10 feet away is preferable to a structural steel bond located 150 feet away The reco...

Страница 35: ...terminated If several ASCs are installed in one enclosure soft ground the shield of the cable that enters the enclosure within one inch of the entry point You must make the shield continuous within the enclosure but do not earth ground it inside the enclosure When you connect the shield through a 560 pF capacitor to an ASC in a metal enclosure terminate the shield on the metal enclosure at the poi...

Страница 36: ...th Shielded Cable ASC EXAMPLE1 REF N2 N2 MM CVT101 x or Pane LTD Companion Enclosure ASC Enclosure REF N2 N2 Enclosure Ground within 1 inch of enclosure s EXIT HG Ground within 1 inch of enclosure s ENTRY SG Ground within 1 inch of enclosure s ENTRY N2 Bus N2 Bus SG HG HG Notes Hard ground HG the N2 Bus shield within 1 inch of each enclosure Soft ground SG the N2 Bus shield within 1 inch of enteri...

Страница 37: ... 17 N2 Bus with Some Devices in Same Enclosure Other Devices in Separate Enclosure VAV LCP AHU Companion PC or Panel LTD N2 Bus HG SG N2 Bus N2 Bus Metal Enclosure HG M100C UNT EXAMPLE2 SG SG HG Zone Bus Metal Case N2 Bus Metal Enclosure N2 Bus HG Notes Hard ground HG the N2 Bus shield within 1 inch of each enclosure Soft ground SG the N2 Bus shield within 1 inch of entering enclosure with a 560 p...

Страница 38: ...res Notes Hard ground HG the N2 Bus shield within 1 inch of each enclosure Soft ground SG the N2 Bus shield within 1 inch of entering the enclosure with a 560 pF capacitor UNT LCP AHU Companion PC or Panel LTD N2 Bus HG SG N2 Bus N2 Bus Metal Enclosure HG VAV EXAMPLE3 Metal Enclosure AHU N2 Bus HG N2 Bus N2 Bus SG SG Tape back shield Figure 18 N2 Bus with Devices Divided in Two Separate Enclosures...

Страница 39: ...er of these ways Connect an Metal Oxide Varistor MOV across the UNT supply transformer primary The MOV must be rated appropriately for the line voltage For your application refer to Table 7 and select the correct MOV Or use a Split Bobbin transformer rather than a standard non isolated transformer to attenuate electrical noise For 120 VAC line applications we recommend the AS XFR100 1 as a step do...

Страница 40: ...21ZOV251RA72 D6321ZOV301RA105 D6521ZOV301RA150 D6921ZOV301RA80 None Mallory VSAC14DK201U VSAC20DK201U VSAC14DK391U VSAC20DK391U VSAC14DK471U VSAC20DK471U VSAC14DK621U VSAC20DK621U Marcon TNR15G211KM TNR23G201KM TNR23G211KM TNR15G391KM TNR23G391JM TNR23G391KM TNR15G471K TNR23G471K None Oneida CKE OZ130LA10A OZ130LA20A OZ130LA20B OZ21L221 0216NR14 3 0216NR20 4 OZ250LA20A OZ250LA40A OZ250LA40B OZ21L4...

Страница 41: ...isy wire which is typically from switched line voltage loads gas ignition and line voltage distribution 3 Properly place equipment and route wiring to separate quiet wiring from noisy wiring Also use proper terminal and wire sizes to establish tight reliable electrical connections 4 Use suppression devices on inductive or noisy loads 5 Establish a low impedance connection to earth 6 If possible in...

Страница 42: ...42 Introduction ASC and N2 Bus Networking and Troubleshooting Guide ...

Страница 43: ...feet 150 meters with 18 AWG cable or 50 feet 15 meters with 24 AWG cable Maximum Number of Devices 24 Range of Addresses 0 to 63 Voltages Logic High Voltage Logic Low Voltage 4 VDC minimum approx 1 VDC maximum approx Data Transmission 1 Start Bit low level 8 Data Bits least significant bit first 1 Stop Bit high level Each subordinate device e g M100C monitors the bus and responds only to messages ...

Страница 44: ... as well as an electrical interface The internal microcontroller allows the RS 232 port to operate at 1200 baud while the LCP side operates at 600 baud The connection to the LCP is made with a 4 pin connector The Cable Pro needs an external 9 12 VDC VAC 60 mA power transformer for LCP service port communication e g Radio Shack 12 VDC transformer kit 273 1652 A DB9 or DB25 connector is used to conn...

Страница 45: ... cable is permanently attached to the Cable Pro making PC attachment more convenient The unit has protection against earth ground faults that may be introduced into the system Two diagnostic LEDs indicate the status of communication of the Zone Bus and the LCP RS 232 connection Descriptions of these LEDs are printed on the unit and summarized in Table 9 CBLPRO 2 To Power To LCP 12 VDC To ASC Zone ...

Страница 46: ...n Shorted to Zone Bus Off On LCP Common Shorted to LCP Data Terminal or Interrupted Communication Off Off No Power or No Connection to Active Zone Bus or No Power or Communication for LCP The AS CBLCON 0 Cable Connector Figure 21 is a cable connecting device that accepts the different sizes of telephone cable connectors used with the ASC products so that they are able to communicate It also monito...

Страница 47: ...tight and proper connections between the laptop PC Cable Pro and the ASC 5 Invalid message size The size of the message sent does not correspond to the type of message sent 11 Invalid command The command issued is not valid for the data type 14 Not ready The ASC cannot process this message at this time For example the EEPROM is not functioning properly Cycle power on the ASC If problem persists re...

Страница 48: ...nt is defective A noisy wire adjacent to the Zone Bus can also cause communication errors Noise can be periodically induced into the Zone Bus thereby causing sporadic communication failures between the laptop and the ASC Most often noisy lines cause intermittent disruption not total loss of communication For more information on the HVAC PRO for Windows refer to the HVAC PRO for Windows User s Manu...

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