4–20 mA vs 0–10 V vs SSI: Choosing a Position Sensor Output

Why the Output Choice Matters More Than the Sensor

Two position sensors with identical mechanics can behave completely differently on the same machine, purely because of how they transmit the measurement. The output decides:

• how far the cable can run before noise ruins the signal;
• what input card your PLC or controller needs;
• whether position survives a power cycle;
• how many sensors you can put on one cable;
• and, often, the price.

Here is how to choose without guessing.

Option 1: Voltage Divider (Ratiometric) — Cheapest, Shortest Range

A potentiometer wired as a three-terminal divider. Output is a fraction of the supply voltage, so it is ratiometric: if the supply sags, the reading stays correct as long as the ADC uses the same reference.

• Pros: three wires, no electronics, lowest cost, works with any microcontroller ADC.
• Cons: cable length limited to a few metres, sensitive to load impedance, no line-break detection.
• Use when: the sensor sits inside the same enclosure as the controller, or you are building high-volume OEM equipment.

Typical models: DWS1A (0–1500 mm), SG1 (0–5 inch), SM1/SM2 (0–25 inch).

Option 2: 0–10 VDC — Convenient, Distance-Limited

A conditioned voltage output, usually from a DC LVDT or an OEM draw wire sensor.

• Pros: universally supported by analogue input cards; simple to scale; no loop supply needed.
• Cons: voltage drop and induced noise over distance; a 10 V signal is only 10 V, so a 200 mV noise spike is 2 % error. Practical limit: about 10–15 m of cable in a clean cabinet, less near drives.
• Use when: sensor-to-cabinet distance is short and the electrical environment is benign.

Typical models: DC750-SE750 (0.05–20 inch, 0–10 VDC), SKD, SR1V, PTL-ARTSD (selectable 0–5 V / 0–10 V / 2–10 V / ±5 V / ±10 V).

Option 3: 4–20 mA — The Industrial Default

A current loop. Because the same current flows through the entire loop, cable resistance does not change the reading, and induced voltage noise is largely rejected.

• Pros: long runs (hundreds of metres), strong noise immunity, live zero at 4 mA so a broken wire reads as a fault rather than as zero position, intrinsically safe variants for hazardous areas.
• Cons: needs a loop supply and a current input card; slightly more expensive sensor; one signal per pair of wires.
• Use when: the machine is large, the cable is long, VFDs are nearby, or the area is classified. This is the safe default for industrial retrofits.

Typical models: PT9420 and PT9420EX (600–1700 inch, hazardous-area certified), SKD, DWS1MA, PTL-ARTSD, RT8420 rotary (0.125–200 turns), IT9420 tilt (45–240°).

Option 4: SSI (Synchronous Serial Interface) — Absolute and Digital

A clock-and-data pair that transmits an absolute position word. No analogue conversion anywhere in the chain.

• Pros: absolute position available immediately at power-up, no drift, high resolution, robust over tens of metres, error bits for diagnostics.
• Cons: requires an SSI input on the controller (or a gateway); point-to-point only, one sensor per channel; slightly higher sensor cost.
• Use when: the machine must know its position the instant it powers on, or when resolution matters more than cost.

Typical models: DWS1S (SSI/BiSS, ±0.1 % FS), SR1H, SGJ, SKH, and 25 models across our catalogue offer SSI.

SSI vs incremental: an incremental encoder reports change, so you must home the axis after every power loss. SSI reports where you are. For a lift, a press or any vertical axis, that difference is a safety issue, not a convenience.

Option 5: Incremental Encoder / Pulse — For Motion Control

Quadrature A/B (sometimes with Z index) pulses. Standard input on every servo drive and motion controller.

• Pros: extremely high resolution, near-zero latency, native to motion control.
• Cons: relative measurement — needs homing; pulse frequency limits cable length and maximum speed.
• Use when: the axis is closed-loop controlled and homing is already part of the sequence.

Typical models: SE1 (25–50 inch, ±0.050 inch), SR1E (125–175 inch), CH25 rotary, A125/A250 encoder accessories.

Option 6: Fieldbus (RS-485 / Modbus / CAN Bus)

Multiple sensors share one cable, each with an address. Diagnostics travel with the data.

• Pros: fewer cables, per-sensor status, remote range changes, no analogue scaling drift.
• Cons: needs protocol support on the controller; polling latency; more configuration work.
• Use when: many sensors along one machine, or the controller already speaks the protocol.

Typical models: PTL-TSK-T080 (0–15 mm, Modbus RS-485), DLBB digital LVDT probe (1/2/5 mm, RS-485, ±0.1 % of reading), plus CAN Bus variants on selected position sensors.

Comparison at a Glance

Five Practical Rules

1. Long cable or noisy plant → current or digital. Never 0–10 V over 30 m next to a drive.
2. Vertical axis → absolute. SSI or a bus, not incremental. A power blip should not lose the height of a lift.
3. Hazardous area → 4–20 mA with the right certification, and check whether the barrier changes your loop voltage budget.
4. Many sensors → bus. Ten analogue channels is ten cables, ten cards, ten calibration drifts.
5. Resolution is not accuracy. A 24-bit SSI word on a ±0.35 % FS draw wire still gives you ±0.35 % FS. Buy accuracy first, resolution second.

Scaling and Commissioning Notes

• 4–20 mA: confirm your input card's burden resistor. A 250 Ω shunt gives 1–5 V; a 100 Ω gives 0.4–2 V. Check the loop can drive it.
• 0–10 V: use shielded twisted pair, ground the shield at the controller end only, and keep the sensor's 0 V reference tied to the card's analogue common.
• SSI: match clock frequency and data format (binary vs Gray code) exactly. A Gray/binary mismatch produces plausible but wrong numbers — the worst kind of bug.
• Incremental: verify pulse-per-inch before you trust a travel distance. Direction inversion is a one-line fix in software, but only if you notice it.

Frequently Asked Questions

Is 4–20 mA better than 0–10 V? For industrial machines, almost always. It survives long cable runs and noise, and its live zero makes broken wires visible. The exception is a short, clean, in-cabinet run where 0–10 V is simpler and cheaper.

Can I convert 0–10 V to 4–20 mA? Yes, with a signal conditioner or isolator. Just remember you are adding a failure point and a calibration step — buy the right output up front when you can.

What does SSI stand for? Synchronous Serial Interface. It is a point-to-point absolute position protocol, not to be confused with SPI.

Do I lose position when power is cut? With a voltage or current output, yes — the sensor re-reads physical position when power returns, so the value is immediately valid again. With an incremental encoder, no: you lose the count and must home the axis.

Tell Us Your Controller

Send the input card type and cable length, and we will recommend the output variant and the model that supports it — out of 149 position sensors spanning LVDT, draw wire, rotary and tilt.

Browse all position sensors → · Draw wire with 4–20 mA →