When specifying a level sensor, one of the first decisions you’ll face is output type: analogue or digital? Both do the same fundamental job — telling you how much liquid is in a tank, well or channel — but they get the signal to your system in very different ways. Choosing the right one affects wiring cost, cable length, accuracy over distance and how easily the sensor integrates with your controller or logger.
What is an analogue output?
An analogue sensor produces a continuous electrical signal that varies in proportion to the measured level. Common formats include:
- 4–20 mA – the industrial workhorse; a current loop that’s robust over long cable runs and immune to voltage drop
- 0–10 V / 0.5–4.5 V – simple voltage outputs, ideal for shorter runs and many PLC analogue inputs
- mV – a raw, low-level output for systems with their own signal conditioning
Strengths: universally supported, simple to wire into almost any PLC or display, no protocol configuration, real-time continuous signal.
Trade-offs: each sensor typically needs its own dedicated wiring; voltage outputs lose accuracy over long distances; limited built-in diagnostics.
What is a digital output?
A digital sensor sends its reading as data over a communication protocol. The most common in level measurement are:
- SDI-12 – purpose-built for environmental and water monitoring; multiple sensors share one cable
- RS485 (e.g. Modbus) – a rugged industrial bus supporting long distances and many devices on a single line
Strengths: values arrive already in engineering units, high noise immunity, multiple sensors on one cable (reducing wiring), and rich diagnostics such as temperature and status.
Trade-offs: your controller or logger must support the protocol, and there’s a small amount of configuration/addressing to set up.
Head-to-head comparison
Factor | Analogue | Digital |
Typical formats | 4–20 mA, 0–10 V, 0.5–4.5 V, mV | SDI-12, RS485 |
Wiring | One sensor per input | Multiple sensors per bus |
Long cable runs | Excellent (4–20 mA) / limited (voltage) | Excellent |
Integration | Plug-and-play with most PLCs | Requires protocol support |
Diagnostics | Minimal | Extensive |
Best for | Simple, single-point installs | Multi-sensor / data-logging networks |
So which should you choose?
- Choose analogue if you want the simplest possible integration, you’re connecting to a standard PLC analogue input, or you have a single measurement point. 4–20 mA remains the safest choice for long runs.
- Choose digital if you’re building a monitoring network, want values in engineering units with diagnostics, or need several sensors on one cable — common in environmental and water-resource monitoring.
Stork options for both approaches
Stork Solutions’ submersible level sensor range covers both outputs across silicon and ceramic sensing elements:
- Analogue: the SLS-SA (silicon) and SLS-CA (ceramic) support mV, 4–20 mA, 0.5–4.5 V and 0–10 V.
- Digital: the SLS-SD (silicon) and SLS-CD (ceramic) support SDI-12 and RS485.
Not sure which fits your setup? Talk to the Stork Solutions team and we’ll help you match the output to your controller and application.
