How to Choose a Signal Isolator?

If you are confused by terms like ground loop, common mode interference, or different signal types such as 4-20 mA and 0-10 V, you are not alone.

This guide is designed for:

• Engineers working with PLC or DCS systems
• Automation technicians in industrial control panels
• Buyers selecting signal conditioning or isolation modules

In real applications, signal isolators are mainly chosen based on a few key considerations. Below is a quick table of contents — click to go straight to the topic you care about:

• When Do You Need a Signal Isolator?
• Signal Isolator or Signal Conditioner
• Signal Type Matching
• Power Supply Selection
• Channel and Space Requirements
• Environment and Safety
• Performance Comparison

For example, in a factory with variable frequency drives (VFDs), electrical noise can easily distort sensor signals and cause unstable readings. In chemical plants or oil facilities, improper grounding can even damage PLC input modules due to ground loops.

That’s where signal isolators become essential—they stabilize signals, protect equipment, and ensure accurate data transmission.

This article also provides a 30-second selection reference table for purchasers unfamiliar with signal isolator modules. You can match the right product to your application by checking the key specs side by side.

When Do You Need a Signal Isolator?

You need to condition your signal when a sensor signal cannot be directly and reliably used by the controller (PLC, DCS, or display system). The core job of a signal isolator is to provide electrical isolation, which helps block interference, eliminate ground loops, and protect your equipment.

Some signal isolators also convert or split signals. In that case, you're actually looking at an isolated signal conditioner. — It can also convert, split, and protect signals. That means you might actually be talking about a signal conditioning device that includes isolation.

Here are a few simple signs that your signal has a problem:

• The signal types do not match, such as 4-20 mA vs 0-10 V.
• The signal is weak or unstable over long cable distances.
• Electrical noise from devices like VFDs or motors causes signal fluctuation.
• Multiple devices share the same grounding and create ground loop issues.

In short, if the signal is not clean, compatible, or stable for your controller, a signal isolator with conversion is needed.

Signal Isolator or Signal Conditioner – Which One Should You Pick?

Some problems only need a signal conditioner (like an amplifier or converter), not necessarily an isolator.

Signal Isolator Application Guide

Your Problem	Possible Risk	Key Thing to Check
Signal type mismatch (4-20 mA vs 0-10 V)	Won't work at all	Signal type
The signal gets weak after a long distance	Signal loss	Signal type
The thermocouple signal is too small	Can't read it	Special signal type
Multiple sensors interfering with each other (ground loop)	Ground loop damage	Grounding/Environment
The signal gets unstable when a VFD starts up	Data fluctuation	Electromagnetic environment
Mixing different types of signals	The system becomes unstable	System integration

Quick answer for "Thermocouple signal is too small":

A thermocouple outputs a mV-level signal, which a PLC can't read directly. You need a thermocouple transmitter (often built into a signal isolator). It amplifies the signal, handles linearization and cold junction compensation, and converts it to 4-20 mA or 0-10 V. See product examples under "Matching Signal Types" below.

Match Your Signal Type for Your Signal Isolator (Most Important!)

My sensor is a K-type thermocouple. Does your signal isolator support that?

My PLC only takes 4-20 mA. Can you convert it?

This means the sensor outputs a millivolt-level (mV) signal—not a standard analog signal. The PLC’s analog input module can only read 4-20 mA current signals.

This is the first step in choosing the right model. If the signal types don’t match, then all the other specs, like accuracy and isolation voltage, are useless.

If you connect a K-type thermocouple (mV) to a basic signal isolator:

The signal isolator doesn't understand mV signals—its input range is usually 4-20 mA or 0-10 V. So the output is still mV, and your PLC still can't read it.

Ask yourself these questions to know if you need signal type conversion:

• What signal does my sensor output? (4-20 mA, 0-10 V, thermocouple, etc.)
• What signal does my controller accept?
  Sensor not 4-20 mA? A K-type thermocouple outputs only ~0-50 mV — most PLCs can’t read that. The universal signal isolator ATO-TS-TR/TS-TC lists “K/B/S/E thermocouple, Pt100” as input types. That spec tells you it amplifies mV signals to 4-20 mA. If your sensor type is on that list, the mismatch is solved.
  

Follow this simple guide for signal isolator and conditioner selection:

• If they don’t match, you need a conditioning function (from a signal conditioner OR a signal isolator that also converts signals).
• If they match but you have interference or ground loops, it means you need a basic signal isolator (it isolates without changing the signal).
• If they don’t match AND you have interference, it means you need a signal isolator with conversion built in.

What to do if your signal gets weak over a long distance?

If you're using 0-10 V or thermocouple mV signals, the signal can weaken or pick up noise when the cable runs longer than 100 feet (30 meters).

Recommended conversion & isolation approach:

0-10 V voltage signals are usually reliable only up to 100 feet. But 4-20 mA current signals can travel thousands of feet (over 1,000 meters). So the fix is to convert your voltage or mV signal to 4-20 mA at the sensor side.

What you need is a signal isolator with conversion capability—one that turns voltage/mV into 4-20 mA and also provides electrical isolation.

Choose the Power Supply Type for a Signal Isolator

You need to think about whether there is an extra 24 V power cable on site. If there isn’t, and you want something easy, choose loop-powered.

If you want stable performance and strong load capacity, choose a separate power supply.

Type	Pros	Cons	Best For
Loop-powered	No extra power needed	Limited output	Simple systems
External power (24 V)	Stable, strong output	Extra wiring	Industrial systems

Tip:

• Want simplicity? Choose loop-powered.
• Want stability? Choose external power.
  What does "loop-powered" solve? No extra 24 V cable.
  The 4-20 mA signal isolator ATO-SIN-1002S draws all power from the 4-20 mA loop (0 W external), converting it to a 0-10 V output. That number means you can install it without pulling new wires — saves cost and space in crowded panels.

Check Space & Channel Requirements for Signal Isolators

Control panels use DIN rails (35 mm), so size matters.

• Narrow modules (12.5 mm) save space
• Wider modules (17.5 mm) may offer more features

Common configurations:

• 1 input for 1 output
• 1 input for 2 outputs (for PLC + display)
• 2 inputs for 2 outputs (space-saving option)

If you are an engineer working with a DCS (Distributed Control System) for large factories, you have to pay attention to channel density (for example, two inputs and two outputs). Because the system is very big, saving space inside the control cabinet means saving money.

Tip:

If you have many signals, multi-channel signal isolators save space and cost.

Channel numbers tell you what fits. The explosion proof signal isolator ATO-FK-SFX110/112/114 series: 110 = 1-in-1-out, 112 = 1-in-2-out, 114 = 2-in-2-out. The extra spec [Ex ia Ga] ⅡC solves hazardous area compliance — without that number, your plant won’t pass safety inspection.

Consider Environment & Safety

This one step decides whether your equipment will be shut down by safety inspectors or get burned up in extreme environments.

Isolation Voltage

If you run into problems like 'two sensors interfering with each other' or 'the signal goes crazy as soon as the inverter starts up', that means you have ground loop current or electromagnetic interference. The spec you need to pay attention to is isolation voltage.

This shows how much electrical stress the isolator can handle.

• Standard industrial use: ≥ 1500 V recommended
• High interference (motors, VFDs): higher is better

Higher isolation is better protection

How high is enough?

In normal environments, 1500 V isolation is enough. But if you have a VFD (variable frequency drive), going with 2000 V is a safer bet.

So, which product fits this VFD scenario? You don’t necessarily need a specified 2000 V rating — a well-designed loop-powered isolator with strong isolation and proven noise immunity can do the job.

This loop-powered signal isolator ATO-SINIR-502E offers signal conversion and electrical isolation for 4-20 mA/0-20 mA/0-5 V/0-10 V signals. It features strong input/output/power supply isolation to help eliminate ground loops and is suitable for industrial fields with severe signal interference.

What Is 3-Way Isolation?

If your system has both 4‑20 mA and 0‑10 V signals, or if there is a lot of noise from the power supply, what you need is triple isolation (input, output, and power supply are all isolated from each other).

It means full isolation between the following:

• Input
• Output
• Power supply

Choose this if:

• You mix different signal types
• Your system has electrical noise

Do You Need Explosion-Proof Certification?

If you work in:

• Oil & gas
• Chemical plants
• Fuel stations

For dangerous industries (like oil and chemicals), you MUST choose isolators with Ex certification.

Compare Performance

Accuracy

Example: ±0.1% (lower is better)

Temperature Drift (Very Important!)

Shows how much accuracy changes with temperature

Why it matters:

• A cheap signal isolator may work fine at 77 °F (25 °C).
• But at 122 °F (50 °C), readings may drift significantly.

If your control cabinet gets hot, always check temperature drift.

Response Time

Application	Speed Requirement
Temperature/pressure	Not critical
Speed/vibration	Fast (≤ 2 ms)

Tip:

Most applications don't need ultra-fast response.

For experienced engineers: view the full isolated signal conditioning product catalog and datasheets for all technical specifications.

Final Checklist for Choosing a Signal Isolator

StepWhat to CheckAction1Signal typeMust match input & output2Power supplyLoop or external3Channels & sizeFit your panel4EnvironmentIsolation voltage/safety5Accuracy & driftStable under temperature6Response timeOnly if high-speed signals

 

3 Key Rules for Isolated Signal Conditioning

• Always match signal types first.
• Choose a higher isolation voltage in noisy environments.
• In hot environments, temperature stability matters more than accuracy.

Conclusion

Choosing the right signal isolator doesn’t have to be complicated.

If you focus on:

• Signal compatibility
• Electrical protection
• Environmental conditions

You can quickly find the right solution for your system.

If you need help, provide these details when contacting a supplier:

• Sensor type
• Output signal (e.g., 4-20 mA, 0-10 V)
• Controller/PLC input type

30-Second Selection Reference Table

Type	Model	Best For	Key Feature	Price
Universal	ATO-SIN-1002S	Loop-powered, 4-20 mA input to 0-10 V output	No external power needed; best value	$96.88
Industrial	ATO-SINIR-502E	Harsh industrial environments	Switch between loop or external 24 V power, high isolation & anti-interference	$122.13
Multi-function	ATO-TS-TR/TS-TC (ATO-SIGNI-402E)	Special signals like thermocouple (K/B/S/E) or RTD (Pt100)	Universal converter; input to 0-10 V or 4-20 mA output	$101.07
Explosion-proof	ATO-FK-SFX110/112/114	Chemical plants, oil & gas, hazardous areas	Certified [Ex ia Ga] ⅡC — safe for dangerous locations	$112.84

About signal isolator ATO-FK-SFX110/112/114:

• If you need basic 1-to-1 isolation, then choose model 110.
• If you need to split one signal to two receivers, then choose model 112.
• If you need to handle two independent signals in a single module, choose model 114.

This will help you get the best recommendation faster.

If you have special requirements such as an LCD real-time display or USB parameter adjustment, please feel free to contact us, ATO Automation, for customization.