CCST CCST Communications & Networking in Control Systems 2 — Questions and Answers
Question 1: Which Foundation Fieldbus segment type operates at 31.25 kbit/s and is intrinsically safe for use in hazardous areas?
- FF HSE
- FF H1 (Correct answer)
- PROFINET
- DeviceNet
Correct answer: FF H1
Foundation Fieldbus H1 operates at 31.25 kbit/s and can be powered intrinsically safely, making it suitable for Zone 0/1 hazardous locations.
Question 2: In Modbus RTU communication, what is the function of the CRC (Cyclic Redundancy Check) appended to each message frame?
- Encrypting the message payload
- Detecting transmission errors in the data frame (Correct answer)
- Setting the baud rate for the next frame
- Addressing the destination slave device
Correct answer: Detecting transmission errors in the data frame
The CRC in Modbus RTU is a 16-bit error-detection code that allows the receiver to identify corrupted data frames.
Question 3: What is the role of a Device Type Manager (DTM) in an FDT/DTM framework used in modern field device management?
- It acts as the physical gateway between Ethernet and fieldbus
- It provides a device-specific software component for configuration and diagnostics within an FDT frame application (Correct answer)
- It assigns IP addresses to field devices
- It stores historian data for trending
Correct answer: It provides a device-specific software component for configuration and diagnostics within an FDT frame application
A DTM is a device-specific software plug-in that runs inside an FDT Frame application to provide full configuration, calibration, and diagnostic access to a field instrument.
Question 4: When configuring a Modbus TCP/IP connection, which default TCP port number is used?
- 80
- 443
- 502 (Correct answer)
- 1024
Correct answer: 502
Modbus TCP/IP uses TCP port 502 as its standard registered port for communication between master and slave devices.
Question 5: Which industrial protocol is specifically designed for time-sensitive applications and uses IEEE 802.1AS for clock synchronization?
- Modbus RTU
- PROFINET IRT (Correct answer)
- HART 5
- DNP3
Correct answer: PROFINET IRT
PROFINET IRT (Isochronous Real-Time) uses IEEE 802.1AS Precision Time Protocol for sub-microsecond clock synchronization to meet strict motion control timing requirements.
Question 6: A technician observes excessive collisions on a legacy industrial Ethernet segment. What is the most likely cause?
- Devices operating in full-duplex mode
- Devices operating in half-duplex mode on a shared hub (Correct answer)
- Too many VLANs configured
- Incorrect subnet mask
Correct answer: Devices operating in half-duplex mode on a shared hub
Collisions occur in half-duplex shared Ethernet (hub-based) environments where only one device can transmit at a time, and simultaneous transmissions cause collisions.
CCST CCST Communications & Networking in Control Systems 2
Which Foundation Fieldbus segment type operates at 31.25 kbit/s and is intrinsically safe for use in hazardous areas?