medium BACnet exam questions

Medium level questions

1. Q01

   The BACnet Multistate Value (MSV), Multistate Input (MSI) and Multistate Output (MSO) objects encode enumerations with several states (3 or more discrete values), such as HVAC modes (Comfort/Standby/Eco) or system states (Auto/Manual/Off).

   TrueFalse

   1. Object types· Multistate Value· Medium

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   Correct answer

   True

   Learning tip

   The split between Binary and Multistate is conceptual: Binary objects (BV, BI, BO) carry 2 states (on/off, true/false), whereas Multistate objects (MSV, MSI, MSO) carry 3 or more enumerated states. A typical MSV represents an HVAC mode such as {Comfort, Standby, Economy, Building Protection} coded as 1, 2, 3, 4, with the State_Text array supplying the human-readable labels. This avoids ad-hoc conventions on AV (e.g. 1=on, 2=off, 3=auto with hidden meanings) and keeps the BMS UI consistent across vendors.

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2. Q02

   BACnet defines standardised BackupAndRestoreFile services that let a BMS save and restore the full configuration of a device (parameters, programming, mappings) in case of hardware replacement.

   TrueFalse

   7. Backup & Restore· Konfigurations-Backup· Medium

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   Correct answer

   True

   Learning tip

   BACnet Backup and Restore (Clause 19.1, Backup and Restore Procedure) relies on ReinitializeDevice to start the backup or restore procedure and AtomicReadFile/AtomicWriteFile to transfer the configuration through a File Object. The typical workflow is: the BMS starts a backup, the device serialises its configuration into the File Object, and the BMS downloads the file; on hardware replacement, the new device is installed and its IP remapped, the backup file is uploaded, and the device restores its configuration. The mechanism is essential for B2B maintenance in production environments.

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3. Q03

   The Niagara Framework (Tridium / Honeywell) is a multi-protocol software platform widely used in modern tertiary BMS, natively integrating BACnet (IP, MS/TP, SC), Modbus, KNX, OPC UA and others.

   TrueFalse

   9. Integration· Niagara Framework· Medium

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   Correct answer

   True

   Learning tip

   Niagara Framework is an integration ecosystem for BMS, structured around the JACE controller hardware (Java Application Control Engine), the Workbench Java engineering tool, a portfolio of drivers (BACnet, Modbus, KNX, OPC UA, MQTT, OEM), a semantic data model based on Project Haystack tagging and a configurable web HMI for visualisation. It is heavily used in the United States (Honeywell) and increasingly in Europe alongside Schneider EcoStruxure and Siemens Desigo CC. Familiarity with Niagara is a baseline skill for medium-to-large tertiary B2B projects.

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4. Q04

   Wireshark ships with a native BACnet/IP dissector that allows full inspection of frames (services, objects, properties) once captured from the network; the most common display filter is "bacapp" (BACnet Application layer).

   TrueFalse

   12. Diagnostics· Wireshark BACnet· Medium

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   Correct answer

   True

   Learning tip

   Wireshark is the de facto tool for debugging BACnet traffic: useful filters include bacapp, bvlc and bacnet, and the dissector decodes ReadProperty exchanges into human-readable object, property and value fields. It also provides per-conversation statistics (who talks to whom and at what rate) and lets you follow a single transaction end to end. To capture effectively, use a switch port mirror or a network TAP; a PC plugged directly into the BACnet VLAN will only see broadcasts plus its own unicast traffic.

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5. Q05

   The standard cable for BACnet MS/TP is an AWG 18-22 shielded twisted-pair with a 120 ohm characteristic impedance and capacitance below 30 pF/ft (98 pF/m), covering distances up to 1200 m at 9600 baud.

   TrueFalse

   22. Practical· MS/TP-Kabelspezifikation· Medium

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   Correct answer

   True

   Learning tip

   Typical MS/TP cable specifications are: AWG 18-22 conductors (18 is more robust, 22 is more economical), 120 ohm characteristic impedance (matching standard RS-485), capacitance no greater than 30 pF/ft (a higher value shortens the maximum reach), and either foil or braided shielding (foil is sufficient indoors). Common reference products include Belden 8761 / 9841 / 9842 and Liberty Cable 18AWG/120 ohm, priced at roughly 1-3 euro per metre depending on the brand.

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