NPN vs PNP vs Totem Pole vs Line Driver: Which Encoder Output Do You Need?

Two encoders can look identical, share the same size and PPR, and still refuse to work with your PLC. The difference is the output circuit. Getting it right is the single most important step when ordering an incremental encoder. This guide explains the four common output types in plain terms and shows the matching VXT encoder for each.

The short answer

Your controller input	Choose this output	VXT example
PLC input configured for NPN sensors (most common in India)	NPN open collector	VXT-E40S06-1024-NPN
PLC input configured for PNP sensors	PNP open collector	VXT-E40S06-1024-PNP
Not sure, or mixed customer base	Totem pole (push-pull)	VXT-E50S08-1024-T
Servo drive, motion controller, CNC, long cable	Line driver (RS-422)	VXT-E40S06-1024-L, VXT-E58S10-5000-L

NPN open collector

An NPN output switches the signal line to 0 V when active. It sinks current. The input on the other side must provide the current, either through its own internal circuit (inputs configured for NPN sensors) or through a pull-up resistor to +V.

• Pros: the most widely used encoder output in Indian panels; works on any supply from 8 to 26 V DC on VXT models; simple and robust.
• Watch out for: without a pull-up, you will not see a voltage on a multimeter, which confuses many first-time installers. Rise time depends on the pull-up resistor and cable length, so keep cables reasonably short at high pulse rates.
• VXT models: VXT-E40S06-0500-NPN, VXT-E40S06-1024-NPN, VXT-E38S06-0360-NPN.

PNP open collector

A PNP output switches the signal line to +V when active. It sources current into the input. It suits PLC inputs configured for PNP sensors, which are common in European-designed machines and some OEM panels.

• Pros: direct connection to PNP-type inputs; signal is "high" when active, which is intuitive to test.
• Watch out for: a voltage-type receiver may need a pull-down resistor to 0 V.
• VXT model: VXT-E40S06-1024-PNP.

Totem pole (push-pull)

A totem pole output has two transistors stacked between +V and 0 V. It actively drives the line high and actively drives it low. That gives sharp edges in both directions and means the output works with both NPN-type and PNP-type inputs.

• Pros: universal compatibility with 12 V and 24 V PLC inputs; cleaner edges than open collector at higher frequencies; no external resistor in most cases.
• Watch out for: never connect two totem pole outputs together, and do not connect the output directly to +V or 0 V.
• VXT models: VXT-E50S08-1000-T, VXT-E50S08-1024-T, VXT-E50S08-2500-T.

In model codes from other makers you may see a similar output under different names. For example, Autonics uses the letter "T" for totem pole in codes such as E50S8-1024-3-T-24, "N" for NPN open collector and "L" for line driver.

Line driver (RS-422 differential)

A line driver outputs each channel twice: the signal and its inverted copy (A and /A, B and /B, Z and /Z). The receiver measures the difference between the pair, so noise picked up on the cable cancels out.

• Pros: the best noise immunity; supports long cables; standard input on servo drives, motion controllers and CNC; allows broken-wire detection on many drives.
• Watch out for: needs a differential (RS-422) receiver. It cannot be wired straight into a standard 24 V PLC input. VXT line driver models run on 5 V DC.
• VXT models: VXT-E40S06-1024-L (40 mm), VXT-E58S06-1024-L (58 mm, 6 mm shaft), VXT-E58S10-5000-L (58 mm, 10 mm shaft, 5000 PPR).

Omron uses the suffix "1X" for line driver models in the E6B2-C series (E6B2-CWZ1X), while its NPN open collector version is E6B2-CWZ6C and its PNP version is E6B2-CWZ5B. If you are replacing one of these, match the output type first, then the size and PPR.

How to check what your PLC needs

• Look at the high-speed counter section of the PLC manual. It will state whether the inputs are sink or source type, the input voltage, and the maximum input frequency.
• Check how the input common (COM or S/S terminal) is wired. On many PLCs, wiring the common to +24 V configures the inputs for NPN sensors, and wiring it to 0 V configures them for PNP sensors.
• For servo drives, check the encoder input specification. "Line driver" or "RS-422" means you need a differential encoder.
• If in doubt, choose a totem pole encoder for 24 V PLC inputs.

Common mistakes we see

• Ordering a line driver encoder for a 24 V PLC input. It will not count reliably and can be damaged by 24 V.
• Connecting an NPN encoder to an input configured for PNP sensors. The input never turns on.
• Powering a 5 V line driver encoder from 24 V. Always check the supply rating on the label.
• Leaving the cable shield unconnected, or earthing it at both ends near a VFD.

Frequently Asked Questions

Is NPN or PNP better for an encoder?

Neither is better; they suit different inputs. NPN is more common in Indian panels and with Japanese and Taiwanese PLC brands. PNP is common in European-designed machines. Match the encoder to the input.

Can a totem pole encoder replace an NPN encoder?

In most 12 V and 24 V PLC applications, yes. A totem pole output drives the line both high and low, so it works with inputs configured for NPN or PNP sensors.

Why does my line driver encoder not work with my PLC?

Most standard PLC inputs are single-ended 24 V inputs. A line driver encoder outputs 5 V differential signals and needs an RS-422 receiver, such as a line driver input module or servo drive input.

Which VXT encoder should I stock as a universal spare?

For 24 V PLC applications, the VXT-E50S08-1024-T totem pole encoder covers both NPN-type and PNP-type inputs.

Need help choosing?

Send us your PLC or drive model and we will confirm the right VXT encoder output. Contact us for datasheets, pricing and availability across India.

Omron and Autonics are trademarks of their respective owners. They are mentioned for reference only; VXT is not affiliated with these companies.