Keyence FS Fibre Optic Amplifiers and FU Fibre Units, New Zealand

Keyence / Fibre optic sensors and amplifiers

A fibre optic sensor is two orders. The FU fibre unit is the optics that goes on the machine, and the FS amplifier is the electronics in the panel that holds every setting. Work out which one failed before you order, because they cost very different amounts and only one of them carries your thresholds.

Fibre amplifiers are the highest volume Keyence item we are asked for, usually in banks of six or ten clipped together on a rail.

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Which half failed

Symptom	Usually
Signal weak or intermittent, display still working	The fibre. Damaged, dirty or misaligned
Reading drops when the machine moves	Fibre fatigue in a cable track or at a bend
Display dead or erratic	The amplifier
No output but the display shows detection	Output wiring, or NPN against PNP
Whole bank dead	The main unit, or the supply to it

The fibre is the part that fails most, because it is the part exposed to the machine. It gets crushed, caught, bent tighter than its minimum radius, or fouled with product.

A quick test: clean the fibre ends and check the alignment. On a thru-beam pair, that plus a fresh look at the mounting resolves a good proportion of intermittent sensors and costs nothing.

Main units and expansion units

The distinction that catches people out when ordering into an existing bank.

Amplifiers clip together side by side and share power and connections through the joint. That means they are not all the same part.

	Main unit	Expansion unit
Carries the cable	Yes. Power and output wiring land here	No
Can work alone	Yes	No. It needs a main unit
Position in the bank	One per group	Alongside
Model number	Different, and they are not interchangeable

So ordering by reading the number off the wrong unit in the bank gets you the wrong part. An expansion unit on its own does nothing, and a main unit fitted where an expansion should go brings a cable you have nowhere to put.

Look at which unit the cable comes out of, and count along to the one that failed. Then send us both numbers and the position.

A photo of the whole bank answers all of this at once and is much quicker than describing it.

NPN and PNP

The output type is a letter at the end of the model number, and it has to match the PLC input card.

Situation	Result
Output type matches the input card	Works
Output type does not match	Sensor detects correctly on its own display and the PLC never sees it

That failure is confusing because the sensor is visibly working. The display shows the target, the output LED behaves, and the input stays off.

Read the suffix off a working amplifier in the same bank. They will all be the same type, and that is the fastest way to be certain.

The whole bank must be one type. You cannot mix output types along a connected group, so a replacement has to match its neighbours as well as the PLC.

Copy the settings from next door

The genuinely useful feature, and most people do not know it is there.

Adjacent amplifiers in a bank can transfer their settings to each other. So a replacement clipped into place can take its configuration from a neighbour rather than being taught from scratch.

Situation	Approach
Replacing one of several identical sensors	Copy from a neighbour, then fine tune
Sensors in the bank do different jobs	Copy gets you close, then set the threshold on real product
A single amplifier on its own	Nothing to copy from. Photograph the settings now

The thresholds were set against real product, often by watching a marginal condition and adjusting until it detected reliably. That is the part worth preserving.

So photograph the display of every amplifier while they work. It takes minutes for a whole bank and it is the only record of settings that were arrived at by trial.

Fibre units, and the bit people get wrong

Aspect	Why it matters
Thru-beam or reflective	Two fibres or one. Completely different arrangement
Head shape	Straight, right angle, flat, sleeve, threaded
Spot size and beam	Fine spot for small targets, wide for tolerance
Bend radius	Fibre has a minimum. Tighter and it degrades or breaks
Environment	Heat resistant, chemical resistant and washdown versions exist
Length	Supplied at a length and often trimmed to suit

Cutting fibre

Plastic fibre is routinely cut to length on installation, and how it is cut decides how well it works.

A clean square cut with the proper cutter gives full signal. A cut with side cutters or a knife gives a rough, angled end that scatters light, and the sensor then runs with far less margin than it should.

Symptom	Possible cause
Sensor works but has almost no margin	Poorly cut fibre end
Failed shortly after somebody shortened it	Same
Gradual loss of signal	Dirt on the end face, or fibre fatigue

So if a sensor has been unreliable since it was reinstalled, look at the fibre end. Re-cutting it properly is free and it is frequently the answer.

We supply the cutters as well as the fibre. On a plant that uses fibre sensors in quantity, having one on site is worth it.

Margin is the number worth watching

Underused, and it turns reactive maintenance into planned maintenance.

The amplifier displays a received light value, not just an on or off state. That number tells you how much signal you have above the threshold.

Observation	Meaning
Comfortable margin above threshold	Healthy
Barely above threshold	Will become intermittent as the lens fouls or the fibre ages
Falling over weeks	Contamination or fibre degradation. Clean or replace before it stops

A sensor with almost no margin is a breakdown waiting for a shift. Reading the numbers along a bank during a routine walk takes a minute and shows you which one is about to go.

That is the sort of thing worth doing on a planned stop rather than discovering at three in the morning.

Before ordering a replacement

Symptom	Check first
Intermittent detection	Fibre end cleanliness, alignment and margin
Fails only when the machine moves	Fibre fatigue in the cable track
Sensor sees the target, PLC does not	NPN against PNP, and the output wiring
Whole bank dead	The main unit and its supply
Unreliable since reinstallation	How the fibre was cut
New amplifier behaves differently	Settings. Copy from a neighbour
Gradually worse over months	Contamination on the fibre end

What to send us

The full model number including the last letter, off the unit that failed.

A photo of the whole bank, showing which unit carries the cable.

Whether the amplifier or the fibre failed.

NPN or PNP, or the PLC it wires into.

The fibre type, thru-beam or reflective, and the head shape.

Whether the fibre routes through a moving part.

Whether the environment is hot, wet or chemically aggressive.

What we can supply

Amplifiers. FS series main and expansion units, in NPN and PNP.

Fibre units. FU series in thru-beam and reflective, in the common head shapes, plus heat and chemical resistant versions.

Accessories. Fibre cutters, mounting brackets, sleeves, lenses and end caps.

Related sensors. LV digital laser amplifiers and heads, and LR self contained laser sensors.

Obsolete amplifiers. Where an older bank needs matching rather than replacing entirely.

A sensible fibre sensor spares holding

Item	Why
One main and one expansion amplifier per type	Settings copy from a neighbour, so a spare really is plug and go
Spare fibre units of the common types	The half that actually fails
A fibre cutter	Cheap, and it prevents a whole class of marginal sensors
Photos of every amplifier's settings	Free, and it is the only record

Because this brand is sold direct, the market has very little spare stock in it. On a machine that matters, that argues for holding the amplifier rather than assuming you can buy one on the day.

We buy Keyence sensors

Amplifiers and fibre units both resell well, because the secondary market is thin.

Keep amplifiers with their fibres, keep banks together with the main unit, and keep anything unused in its packaging. See Sell To Us.

Common questions

Can you get a part that is not listed on your site?
Often. On this brand it depends on the item and we will tell you quickly either way.

Do I need the amplifier or the fibre?
Two separate parts. The fibre is the optics on the machine and the amplifier is the electronics holding the settings.

What is the difference between a main and an expansion unit?
The main unit carries the cable and can work alone. An expansion unit cannot.

My sensor detects but the PLC gets nothing.
Check NPN against PNP. The sensor works perfectly and the input never sees it.

Can I set a new amplifier from an old one?
Usually, by copying from an adjacent unit in the same bank.

Why has it been unreliable since we shortened the fibre?
How the fibre was cut. A rough or angled end loses a lot of signal.

What is the lead time?
It varies more on this brand than most. We give you a firm figure with the quote.

Do you quote in NZD?
Yes, in NZD including GST for New Zealand customers.

Send us a photo of the bank

It shows which unit carries the cable, how many are connected and what the settings are. That is most of what we need in one image. Quotes in NZD including GST.

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Industech is an independent supplier of new, surplus and used industrial automation equipment. We are not an authorised distributor of, approved by, sanctioned by, or affiliated with Keyence. Keyence and the product series named here are trademarks of Keyence Corporation. All trademarks, brand names and model numbers are the property of their respective owners and are used here for identification purposes only.