FS-N11N vs FS-N12N vs FS-N40: Keyence Fiber Amplifier Comparison
Short answer: these three are not three versions of the same amplifier. FS-N11N is a main unit that runs on its own; FS-N12N is an expansion unit that only works stacked behind a main unit; FS-N40 is a zero-line expansion unit with no control output at all. If the part you are replacing has its own output wire going to a PLC input, you need FS-N11N - not FS-N12N, and not FS-N40. Everything below is the detail behind that sentence.
FS-N11N vs FS-N12N vs FS-N40 at a glance
| Item | FS-N11N | FS-N12N | FS-N40 |
|---|---|---|---|
| Series | FS-N series | FS-N series | FS-N40 series |
| Type | Standard, 1 output, cable | Standard, 1 output, cable | Zero-line type |
| Main or expansion unit | Main unit runs stand-alone | Expansion unit cannot run alone | Expansion unit cannot run alone |
| Control outputs | 1 × NPN open collector 24 V, 100 mA max | 1 × NPN open collector 24 V, 100 mA max | None - counts as 1 output only when the bank is wired to an FS-MC8N/P or NU series unit |
| External input | - | - | 1 input, 2 ms (ON) / 20 ms (OFF) |
| Response time | 50 µs / 250 µs / 500 µs / 1 ms / 4 ms / 16 ms | 50 µs / 250 µs / 500 µs / 1 ms / 4 ms / 16 ms | 23 µs / 50 µs / 250 µs / 500 µs / 1 ms / 4 ms / 16 ms / 64 ms |
| Light source | Red 4-element LED, APC on/off | Red 4-element LED, APC on/off | Red 4-element LED, 660 nm |
| Supply voltage | 12-24 VDC ±10 % | 12-24 VDC ±10 % | 10-30 VDC |
| Consumption | 900 mW or less (36 mA at 24 V) | 900 mW or less (36 mA at 24 V) | 870 mW or less (34 mA at 24 V) |
| Units per group | 1 main + up to 16 expansion (17 in total) | Counts as one of the 16 | Counts as one of the 16 |
| Weight | Approx. 75 g | Approx. 45 g | Approx. 23 g |
| Mounting | DIN rail | DIN rail, side by side | DIN rail, side by side |
| Order it when | One channel, stand-alone, output wired straight to the PLC | You are adding channels next to an existing FS-N main unit | The bank is read by an FS-MC8N/P or NU series unit and you want the fastest response |
Specifications quoted from Keyence published data. Check the last letter on your own label: N = NPN, P = PNP. FS-N11P and FS-N12P are electrically different parts from the N versions and cannot be swapped at the PLC input.
What each unit really is
FS-N11N - the safe default
A complete amplifier. It has a display, buttons, its own settings, and one NPN open-collector output that sinks 100 mA at 24 V. Mount it on the DIN rail, plug your FU series fiber head into it, teach it once, and it runs. This is the part to order when one sensor channel on a machine has failed and the wire in the terminal block is the output of the amplifier itself.
FS-N12N - one more channel, no brain of its own
Mechanically it sits next to a main unit and shares that unit's display and settings. It has an output of its own, so the PLC still sees a separate signal per channel - but it has no independent configuration and no stand-alone mode. Stacked behind an FS-N11N it is the cheapest way to add detection points; ordered as the only amplifier in the panel it is a dead part. Forty-five grams instead of seventy-five, because the display and the setting buttons are simply not there.
FS-N40 - a channel inside a bank, not an amplifier you point at a PLC
This is where most catalogues mislead. FS-N40 is not the main unit of the FS-N40 series. It is the zero-line expansion unit of that series: 23 g, no display, and no control output terminal. Its signal is carried by the group it belongs to - an FS-MC8N/P multi-channel output unit or an NU series network unit - which is why the manufacturer data sheet notes that it counts as one output only in that configuration. What it does bring is speed and density: response down to 23 µs, eight selectable steps up to 64 ms, and a 10-30 VDC supply range that rides out a sagging 24 V rail.
If you need a stand-alone amplifier from the FS-N40 generation, the part numbers are FS-N41N (main, 1 output) and FS-N43N (main, 2 outputs), with FS-N42N and FS-N44N as their expansion units. Ordering FS-N40 expecting a main unit is the same class of mistake as ordering FS-N12N expecting a stand-alone amplifier: the part arrives, it fits the rail, and nothing switches.
The mistake we see most often
Main unit and expansion unit look almost identical from the front of a panel, and both are labelled "fiber amplifier". The difference only shows up when the machine is powered: an expansion unit with no main unit in its group has no display, no settings and no switching. Two checks settle it in under a minute:
- Look at the terminal block. An output wire landing on the amplifier's own terminal means a part with a control output - FS-N11N or FS-N12N. No output terminal means the signal leaves through the group's MC or NU unit - FS-N40.
- Count the displays in the group. Exactly one unit in a stacked group carries the display and the buttons. That one is the main unit; everything to its right is an expansion unit.
There is also a hard limit worth knowing before you design a bank: one main unit plus up to 16 expansion units, 17 in total, and a dual-output unit counts as two of the 16.
How to choose in three questions
- Does the failed part have its own output wire? No - you need FS-N40, and your panel already has an FS-MC8N/P or NU unit. Yes - go to question 2.
- Is there already a main amplifier with a display in the same group? Yes - FS-N12N is the direct replacement for the failed expansion unit. No - you need FS-N11N.
- Does the application need two switching points per channel, or an external teach input? Yes - you are outside this comparison: the two-output main unit is FS-N13N (2 outputs, 1 external input) with FS-N14N as its expansion unit.
Reading the model number
| Model | What it is |
|---|---|
| FS-N11N / FS-N11P | Standard 1-output main unit, cable, NPN / PNP |
| FS-N12N / FS-N12P | Standard 1-output expansion unit, cable, NPN / PNP |
| FS-N13N / FS-N13P | High-function 2-output main unit, cable, plus 1 external input |
| FS-N14N / FS-N14P | 2-output expansion unit, cable |
| FS-N11CN / FS-N12CN | The same main / expansion pair with an M8 connector instead of a cable |
| FS-N11MN | Main unit with a 1-5 V monitor output, cable |
| FS-N40 | Zero-line expansion unit of the FS-N40 series - no control output |
| FS-N41N / FS-N43N | Main units of the FS-N40 series: 1 output / 2 outputs |
| FS-N42N / FS-N44N | Expansion units of the FS-N40 series: 1 output / 2 outputs |
There is no FS-N13CN and no FS-N13CP: the two-output models exist in cable type only. A supplier quoting you an "FS-N13CN with M8 connector" is quoting a part number that Keyence does not make.
Lead time and supply
We supply all three as genuine Keyence units, sourced to order rather than held on the shelf: lead time is confirmed in the quotation, typically 1-3 weeks, and each unit is inspected before dispatch. If you are down and need the fastest possible route, send the label photo with the full suffix and the quantity in the first message - that is enough for us to confirm the match and the date in one reply.
FS-N questions we get every week
Can I replace FS-N11N with FS-N12N?
No. FS-N12N is an expansion unit: no display, no settings of its own, no stand-alone operation. It only works behind a main unit in the same group.
Can FS-N40 replace FS-N11N?
No. FS-N40 has no control output; its signal is carried by an FS-MC8N/P or NU series unit. Fitting it where a stand-alone amplifier was wired will leave the PLC input dead.
Do these use the fiber heads I already have?
The FS-N and FS-N40 series take FU series fiber heads, so in most cases the existing head, bracket and fiber stay in place and only the amplifier body is replaced. Check the connector on your head - cable type and M8 type bodies are not interchangeable.
How many units can I stack in one group?
One main unit plus up to 16 expansion units, 17 in total. A dual-output unit counts as two of the 16.
Are the units you ship genuine Keyence?
Yes - genuine, sourced to order. We are an independent seller, not an authorised Keyence distributor, so the 12-month warranty is ours as the seller, not a manufacturer warranty.
Looking for the part itself? See the Keyence FS-N11N fiber amplifier - genuine, sourced to order — inspected before shipment, tropicalized for humid climates, 12-month warranty.
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View product →Keyence FS-N41N main unit (FS-N40 series) - genuine, sourced to order
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Disclaimer: the FS-N11N, FS-N12N, FS-N41N and FS-N40 we supply are genuine Keyence products, sourced to order by InverterPLC as an independent seller. We are not an authorised Keyence distributor, no OEM warranty is implied, and the 12-month warranty is our own seller warranty. Brand names and model numbers are the property of their respective owners and are used here for identification only. Specifications are quoted from the manufacturer published data - always confirm the suffix, connector type and output polarity against the label on your own unit before ordering.