Despite advances in digital protocols, the humble 4–20mA analog signal remains the workhorse of industrial instrumentation. From pressure transmitters to valve controllers, this signal format is trusted for one key reason: reliability.
In this article, we’ll explore how 4–20mA loops work, why they still dominate field installations, and the tools every technician should have on hand when working with them.
📏 What Is a 4–20mA Signal Loop?
A 4–20mA loop is a method of transmitting an analog signal from a sensor (like a temperature or pressure transmitter) to a control system like a PLC or DCS. The signal current varies linearly with the measured parameter:
4 mA = lowest measurable value (e.g. 0°C)
20 mA = highest measurable value (e.g. 100°C)
This method is immune to signal loss over long cable runs, and loop integrity can be monitored easily (0 mA = broken wire).
🔧 Why 4–20mA Is Still King
Noise Resistance: Current signals are less susceptible to electrical interference
Simplicity: Easy to implement, no complex protocol or software
Power + Signal: A 2-wire loop can carry both power and signal
Diagnostics: Signal drop below 4 mA indicates a fault
Even in modern smart factories, 4–20mA is often used as a fallback or redundancy signal due to its proven stability.
🛠️ Tools You Need to Work with 4–20mA Loops
To safely and accurately test, simulate, and troubleshoot analog loops, you’ll want a few essential tools. Here are our top Amazon picks:
🧠 Final Thoughts
4–20mA may be decades old, but its simplicity, reliability, and diagnostic value make it irreplaceable in many industrial systems. With the right tools in your bag, you can measure, simulate, and troubleshoot analog loops safely and efficiently.
📦 Ready to upgrade your analog loop toolkit? Check out the trusted tools above and level up your workflow.
✅ Top Pick: Fluke 773 Milliamp Clamp Meter
Specially designed for process technicians, the Fluke 773 allows you to measure 4–20mA signals without breaking the loop—saving time and preventing downtime in critical systems.
✅ Also Recommended: Fluke 117 Clamp Multimeter
Need a versatile clamp meter for AC/DC current and voltage beyond 4–20mA loops? The Fluke 117 offers TRMS accuracy and is ideal for general electrical diagnostics.