PlantFlow 3D › Guides › 4–20 mA vs 0–10 V: which analog signal should you use?
4–20 mA vs 0–10 V: which analog signal should you use?
The practical difference between 4–20 mA current loops and 0–10 V voltage signals: live zero, wire-break detection, noise, cable length and when each one is used.
The same job, two methods
Both signals carry one measurement from a transmitter to a PLC or controller. 0–10 V sends it as a voltage; 4–20 mA sends it as a current, where 4 mA is 0 % and 20 mA is 100 % of the range.
Live zero and broken wires
The biggest difference is the live zero. With 4–20 mA a healthy signal is never below about 3.8 mA, so 0 mA means a broken wire or a failed instrument, and the PLC can raise a fault alarm (NAMUR NE 43). With 0–10 V a broken wire reads 0 V, which looks exactly like a real zero measurement, so the fault can go unnoticed.
Noise and distance
A current is the same everywhere in a series loop, so cable resistance and induced noise affect a 4–20 mA signal much less. That is why it is the standard for field instruments over long cables. 0–10 V is simple and cheap, and is common for short runs inside a panel, for example a speed reference to a VFD or a signal from an HVAC sensor.
Scaling
For both, the value is linear: value = LRV + fraction × (URV − LRV), where the fraction is (mA − 4) / 16 for current and V / 10 for voltage. A 0–10 bar transmitter reading 12 mA or 5 V both mean 5 bar.
Try it yourself
Open PLC & Process. Set the PT-101 fault to “Signal wire broken” (0–10 V) and the LT-101 fault to “Open loop” (4–20 mA), and compare the alarms.
Open the PlantFlow 3D simulator →Safety: this guide explains principles for learning. Real installations must follow the applicable codes, the equipment manufacturer's instructions and the approval of a competent, qualified person. Isolate, lock off and prove dead before touching any circuit.