Best Practices for Fusing Signal Conditioners: Individual vs. Grouping for 24VDC Systems

Question:

Attention, forum enthusiasts! Here's a burning question for those experienced with signal conditioning: Should I fuse each signal conditioner individually, or is it more efficient to group them together? Currently, I’m working on a project that includes 25 signal conditioners—some designed for voltage (0-80V = 4-20mA) and others for current (0-5A = 4-20mA). What do you recommend regarding the 24VDC power supply: should I provide a separate fuse for each unit, group them into sets of five, or use a single fuse for all? This topic seems to spark some debate, and I’ve personally never encountered a situation where a signal conditioner has failed and blown a fuse. I’d appreciate your insights!

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NetNathan inquired: "Hello, fellow forum enthusiasts! When it comes to fusing signal conditioners, should I fuse each one individually or can I group them? I’m currently working on a project that includes 25 signal conditioners—some designed for voltage (ranging from 0-80V to 4-20mA) and others for current (0-5A to 4-20mA). Would it be more effective to fuse the 24VDC power for each unit, in groups of five, or to use a single fuse for the entire setup? This topic seems to provoke debate, as I have yet to experience any signal conditioner failures related to blown fuses. However, we have encountered issues with current sensors that provide a direct 4-20 mA output, where the signal simply disappears, leading to an under-range report. Is there a preferred division for grouping—such as sending signals from your isolators to an analog card equipped with 8 channels or perhaps 4? I’m considering utilizing a power supply that automatically detects short circuits and powers down when needed; it seems that Devicenet power supplies typically have this feature. Would it be advisable to implement a mini breaker that can accommodate all 25 signal conditioners? Alternatively, is there a valid reason to use separate 24V power supplies? Should maintaining functionality in one production line take precedence if another device experiences a trip? Your insights would be greatly appreciated!"

All signal conditioners operate on a unified 24VDC power source. This 24VDC power supply, equipped with short circuit protection from Phoenix Contact QUINT, is specifically allocated for the signal conditioners and the Acromag Analog Input modules. The setup subsequently interfaces via Profinet to the PLC. The signal conditioners effectively convert voltage and current signals into a standardized 4-20mA output for two 16-point Analog Input modules (Acromag XT1233), which feature Profinet communication capabilities to the GE RX3i PLC. Additionally, the Acromag Analog Input modules are protected by fuses for enhanced safety and reliability.

NetNathan stated: "All signal conditioners operate on the same 24V DC power supply, equipped with short circuit protection (Phoenix Contact QUINT). This power supply is solely dedicated to the signal conditioners and Acromag Analog Input modules. From there, the system communicates through Profinet to the PLC. The signal conditioners are responsible for converting voltage and current signals into 4-20mA outputs, which feed into two 16-point Analog Input modules (Acromag XT1233) that feature Profinet connectivity to the GE RX3i PLC. Additionally, the Acromag AI modules come with fusing for added safety. It’s important to note that if your power supply drops to 0V during a short circuit, fuses won't be blown. Typically, you'd have disconnects that allow you to service one instrument while keeping the others powered. Alternatively, you could use knife switch terminal blocks or fusible terminal blocks for this purpose."

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Frequently Asked Questions (FAQ)

FAQ: A2: Fusing each signal conditioner individually offers several advantages, including:

Answer: - Easier fault isolation, allowing you to quickly identify and address issues with specific units. - Enhanced protection, as each unit is independently safeguarded against overcurrent. - Reduced risk of cascading failures, where a fault in one unit does not affect others.

FAQ: A3: Using a single fuse for multiple signal conditioners can simplify the wiring and reduce costs, but it has some downsides:

Answer: - Difficulty in pinpointing which unit caused the fuse to blow, leading to more complex troubleshooting. - Increased risk of losing functionality for multiple units if a fault occurs, affecting the overall system performance.

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