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NX-CT[][][][]

NX-series High-speed Counter Unit

NX-CT[][][][]

High-speed counter unit ideal for edge control, achieving high-speed response and high-resolution performance

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last update: January 5, 2026

General Specifications

Item Specification
Enclosure Mounted in a panel
Grounding methods Ground to 100 Ω or less
Operating
environment		 Ambient operating
temperature		 0 to 55°C
Ambient operating
humidity		 10 to 95% RH (with no icing or condensation)
Atmosphere Must be free from corrosive gases.
Ambient storage
temperature		 -25 to 70°C (with no icing or condensation)
Altitude 2,000 m max.
Pollution degree Pollution degree 2 or less: Conforms to JIS B 3502 and IEC 61131-2.
Noise immunity Conforms to IEC 61000-4-4, 2 kV (power supply line)
Overvoltage category Category II: Conforms to JIS B 3502 and IEC 61131-2.
EMC immunity level Zone B
Vibration resistance Conforms to IEC 60068-2-6.
5 to 8.4 Hz with amplitude of 3.5 mm,
8.4 to 150 Hz, acceleration of 9.8 m/s2
100 min each in X, Y, and Z directions (10 sweeps of 10 min each = 100 min total)
Shock resistance Conforms to IEC 60068-2-27, 147 m/s2, 3 times each in X, Y, and Z directions
Applicable standards *1 cULus: Listed (UL61010-2-201), ANSI/ISA 12.12.01, EU: EN 61131-2, RCM,
and KC (KC Registration)

*1. Refer to the OMRON website (Models with Standards Certification) or ask your OMRON representative for the most recent applicable standards for each model.

Specifications of Individual Units

NX-CT2120

Unit name High-speed Counter Units Model NX-CT2120
Number of channels 2ch/6ch switching External connection
terminals		 Screwless clamping terminal block
(16 terminals × 2)
I/O refreshing method Free-Run refreshing, synchronous I/O refreshing, or task period prioritized refreshing
Indicators TS LED, CH LED, A/B/Z LED, IN LED, OUT LED
3961_sp_2_1
Input signals Counter input terminal:
In 2ch Mode: A-phase 2, B-phase 2, Z-phase 2
In 6ch Mode: A-phase 6
External input terminal: 6
Output signal External output terminal: 6
Counter input format Voltage input (5 V, 24 V)
Pulse Input Method In 2ch Mode: Phase differential pulse (multiplication x1/2/4), pulse + direction, up and down pulse inputs
In 6ch Mode: Single-phase
Counter range -2147483648 to 2147483647
Counter functions
Counter Type Ring counter or linear counter
Counter controls Gate control, counter reset, and counter preset
Latching In 2ch Mode: Counter Latch 2/ch
In 6ch Mode: Counter Latch 1/ch
Measurements Pulse rate measurement and pulse period measurement
Counter Input Specifications (Voltage input)
Input voltage (24 V) 20.4 to 28.8 VDC
(24 VDC +20%/-15%)		 Input voltage (5 V) 4.5 to 5.5 VDC
ON voltage/ON current (24 V) 18.6 VDC min./3 mA min. ON voltage/
ON current (5 V)		 4.5 VDC min./3 mA min.
OFF voltage/OFF current (24 V) 4.0 VDC max./1 mA max. OFF voltage/
OFF current (5 V)		 1.5 VDC max./1 mA max.
Input current (24 V) 5.6 mA typical (24 VDC) Input current (5 V) 5.3 mA typical (5 VDC)
Maximum response frequency In 2ch Mode: A- and B-phase: Single-phase 250 kHz (phase differential pulse input at multiplication x4: 1 MHz), Z-phase: 250 kHz
In 6ch Mode: Single-phase 100 kHz
Internal I/O common processing NPN
I/O power supply method Supply from the NX Bus
External power supply output (5 V) *1 Output voltage: 4.9 to 5.25 VDC (5 VDC +5%/-2%)
Output current: 500 mA/channel min., 1 A/unit min.
External Input Specifications
Input voltage 20.4 to 28.8 VDC
(24 VDC +20%/-15%)		 ON voltage/
ON current		 15 VDC min./3 mA min.
Input current 3.3 mA typical (24 VDC) OFF voltage/
OFF current		 5.0 VDC max./1 mA max.
ON/OFF response time 1 μs max./1 μs max.
Internal I/O common processing NPN
I/O power supply method Supply from the NX Bus
External Output Specifications
Rated voltage 5 to 24 VDC
Load voltage range 4.75 to 28.8 VDC Residual voltage 0.6 V max.
Maximum value of load current 0.5 A/point, 1.8 A/Unit Leakage current 0.1 mA max.
ON/OFF response time 1 μs max./3 μs max. (at load current 7 to 500 mA)
Internal I/O common processing NPN Load Short-circuit
Protection		 None
I/O power supply method External supply, 4.75 to 28.8 VDC
Current consumption from I/O power supply 20 mA max.
Dimensions 24 (W) × 100 (H) × 71 (D) Isolation method Photocoupler isolation
Insulation resistance 20 MΩ min. between isolated
circuits (at 100 VDC)		 Dielectric strength 510 VAC between isolated circuits
for 1 minute at a leakage current of
5 mA max.
NX Unit power consumption • Connected to a CPU Unit
1.45 W max.
• Connected to
Communications Coupler Unit
1.05 W max.		 Current consumption
from I/O power supply		 Unit current consumption: 20 mA max.
External 5 V power supply
consumption: 0.25 × external 5 V
power supply current consumption *2
Weight 140 g max.
Circuit layout Count input, external input
3961_sp_2_2


External output
3961_sp_2_3
Installation orientation and restrictions Refer to NX-series High-speed Counter Units User's Manual (Man. No. W647).
Terminal connection diagram Refer to Terminal Block Arrangement and Wiring Example on Data Sheet.

*1. When counter input is input voltage (24 V), external power supply (5 V) cannot be used.
*2. Use this formula to convert 5 V power supply current consumption to 24 V power supply current consumption.

NX-CT2220

Unit name High-speed Counter Units Model NX-CT2220
Number of channels 2ch/6ch switching External connection
terminals		 Screwless clamping terminal block
(16 terminals × 2)
I/O refreshing method Free-Run refreshing, synchronous I/O refreshing, or task period prioritized refreshing
Indicators TS LED, CH LED, A/B/Z LED, IN LED, OUT LED
3961_sp_3_1
Input signals Counter input terminal:
In 2ch Mode: A-phase 2, B-phase 2, Z-phase 2
In 6ch Mode: A-phase 6
External input terminal: 6
Output signal External output terminal: 6
Counter input format Voltage input (5 V, 24 V)
Pulse Input Method In 2ch Mode: Phase differential pulse (multiplication x1/2/4), pulse + direction, up and down pulse inputs
In 6ch Mode: Single-phase
Counter range -2147483648 to 2147483647
Counter functions
Counter Type Ring counter or linear counter
Counter controls Gate control, counter reset, and counter preset
Latching In 2ch Mode: Counter Latch 2/ch
In 6ch Mode: Counter Latch 1/ch
Measurements Pulse rate measurement and pulse period measurement
Counter Input Specifications (Voltage input)
Input voltage (24 V) 20.4 to 28.8 VDC
(24 VDC +20%/-15%)		 Input voltage (5 V) 4.5 to 5.5 VDC
ON voltage/ON current (24 V) 18.6 VDC min./3 mA min. ON voltage/
ON current (5 V)		 4.5 VDC min./3 mA min.
OFF voltage/OFF current (24 V) 4.0 VDC max./1 mA max. OFF voltage/
OFF current (5 V)		 1.5 VDC max./1 mA max.
Input current (24 V) 5.6 mA typical (24 VDC) Input current (5 V) 5.3 mA typical (5 VDC)
Maximum response frequency In 2ch Mode: A- and B-phase: Single-phase 250 kHz (phase differential pulse input at multiplication x4: 1 MHz), Z-phase: 250 kHz
In 6ch Mode: Single-phase 100 kHz
Internal I/O common processing PNP
I/O power supply method Supply from the NX Bus
External power supply output (5 V) *1 Output voltage: 4.9 to 5.25 VDC (5 VDC +5%/-2%)
Output current: 500 mA/channel min., 1 A/unit min.
External Input Specifications
Input voltage 20.4 to 28.8 VDC
(24 VDC +20%/-15%)		 ON voltage/
ON current		 15 VDC min./3 mA min.
Input current 3.3 mA typical (24 VDC) OFF voltage/
OFF current		 5.0 VDC max./1 mA max.
ON/OFF response time 1 μs max./1 μs max.
Internal I/O common processing PNP
I/O power supply method Supply from the NX Bus
External Output Specifications
Rated voltage 5 to 24 VDC
Load voltage range 4.75 to 28.8 VDC Residual voltage 0.6 V max.
Maximum value of load current 0.5 A/point, 1.8 A/Unit Leakage current 0.1 mA max.
ON/OFF response time 1 μs max./3 μs max. (at load current 7 to 500 mA)
Internal I/O common processing PNP Load Short-circuit
Protection		 None
I/O power supply method External supply, 4.75 to 28.8 VDC
Current consumption from I/O power supply 30 mA max.
Dimensions 24 (W) × 100 (H) × 71 (D) Isolation method Photocoupler isolation
Insulation resistance 20 MΩ min. between isolated
circuits (at 100 VDC)		 Dielectric strength 510 VAC between isolated circuits
for 1 minute at a leakage current of
5 mA max.
NX Unit power consumption • Connected to a CPU Unit
1.45 W max.
• Connected to
Communications Coupler Unit
1.05 W max.		 Current consumption
from I/O power supply		 Unit current consumption: 20 mA max.
External 5 V power supply
consumption: 0.25 × external 5 V
power supply current consumption *2
Weight 140 g max.
Circuit layout Count input, external input
3961_sp_3_2


External output
3961_sp_3_3
Installation orientation and restrictions Refer to NX-series High-speed Counter Units User's Manual (Man. No. W647).
Terminal connection diagram Refer to Terminal Block Arrangement and Wiring Example on Data Sheet.

*1. When counter input is input voltage (24 V), external power supply (5 V) cannot be used.
*2. Use this formula to convert 5 V power supply current consumption to 24 V power supply current consumption.

NX-CT2320

Unit name High-speed Counter Units Model NX-CT2320
Number of channels 2ch/6ch switching External connection
terminals		 Screwless clamping terminal
block (16 terminals × 2)
I/O refreshing method Free-Run refreshing, synchronous I/O refreshing, or task period prioritized refreshing
Indicators TS LED, CH LED, A/B/Z LED, IN LED, OUT LED
3961_sp_4_1
Input signals Counter input terminal:
In 2ch Mode: A-phase 2, B-phase 2, Z-phase 2
In 6ch Mode: A-phase 6
External input terminal: 6
Output signal External output terminal: 6
Counter input format Line receiver input
Pulse Input Method In 2ch Mode: Phase differential pulse (multiplication x1/2/4), pulse + direction, up and down pulse inputs
In 6ch Mode: Single-phase
Counter range -2147483648 to 2147483647
Counter functions
Counter Type Ring counter or linear counter
Counter controls Gate control, counter reset, and counter preset
Latching In 2ch Mode: Counter Latch 2/ch
In 6ch Mode: Counter Latch 1/ch
Measurements Pulse rate measurement and pulse period measurement
Counter Input Specifications (line receiver input)
Input voltage EIA standard RS-422-A
line driver levels		 High-level input
voltage		 VIT+: 0.1 V min.
Input impedance 120 Ω ±5% Low-level input
voltage		 VIT-: -0.1 V max.
Hysteresis voltage Vhys (VIT+ - VIT-): 60 mV
Maximum response frequency In 2ch Mode: A- and B-phase: Single-phase 1 MHz (phase differential pulse input x4: 4 MHz), Z-phase: 1 MHz
In 6ch Mode: Single-phase 100 kHz
External power supply output (5 V) *1 Output voltage: 4.9 to 5.25 VDC (5 VDC +5%/-2%)
Output current: 500 mA/channel min., 1 A/unit min.
External Input Specifications
Input voltage 20.4 to 28.8 VDC
(24 VDC +20%/-15%)		 ON voltage/
ON current		 15 VDC min./3 mA min.
Input current 3.3 mA typical (24 VDC) OFF voltage/
OFF current		 5.0 VDC max./1 mA max.
ON/OFF response time 1 μs max./1 μs max.
Internal I/O common processing NPN
I/O power supply method Supply from the NX Bus
External Output Specifications
Rated voltage 5 to 24 VDC
Load voltage range 4.75 to 28.8 VDC Residual voltage 0.6 V max.
Maximum value of load current 0.5 A/point, 1.8 A/Unit Leakage current 0.1 mA max.
ON/OFF response time 1 μs max./3 μs max. (at load current 7 to 500 mA)
Internal I/O common processing NPN Load Short-circuit
Protection		 None
I/O power supply method External supply, 4.75 to 28.8 VDC
Current consumption from I/O power supply 20 mA max.
Dimensions 24 (W) × 100 (H) × 71 (D) Isolation method Photocoupler isolation
Insulation resistance 20 MΩ min. between
isolated circuits
(at 100 VDC)		 Dielectric strength 510 VAC between isolated circuits
for 1 minute at a leakage current
of 5 mA max.
NX Unit power consumption • Connected to a CPU Unit
1.45 W max.
• Connected to
Communications Coupler
Unit 1.1 W max.		 Current consumption
from I/O power supply		 Unit current consumption: 30 mA max.
External 5 V power supply
consumption: 0.25 × external 5 V
power supply current consumption *2
Weight 140 g max.
Circuit layout Count input, external input
3961_sp_4_2


External output
3961_sp_4_3
Installation orientation and restrictions Refer to NX-series High-speed Counter Units User's Manual (Man. No. W647).
Terminal connection diagram Refer to Terminal Block Arrangement and Wiring Example on Data Sheet.

*1. External power supply (5 V) may be unavailable due to installation orientation or ambient operating temperature. Refer to NX-series High-speed Counter Units User's Manual (Man. No. W647).
*2. Use this formula to convert 5 V power supply current consumption to 24 V power supply current consumption.

NX-CT2420

Unit name High-speed Counter Units Model NX-CT2420
Number of channels 2ch/6ch switching External connection
terminals		 Screwless clamping terminal
block (16 terminals × 2)
I/O refreshing method Free-Run refreshing, synchronous I/O refreshing, or task period prioritized refreshing
Indicators TS LED, CH LED, A/B/Z LED, IN LED, OUT LED
3961_sp_5_1
Input signals Counter input terminal:
In 2ch Mode: A-phase 2, B-phase 2, Z-phase 2
In 6ch Mode: A-phase 6
External input terminal: 6
Output signal External output terminal: 6
Counter input format Line receiver input
Pulse Input Method In 2ch Mode: Phase differential pulse (multiplication x1/2/4), pulse + direction, up and down pulse inputs
In 6ch Mode: Single-phase
Counter range -2147483648 to 2147483647
Counter functions
Counter Type Ring counter or linear counter
Counter controls Gate control, counter reset, and counter preset
Latching In 2ch Mode: Counter Latch 2/ch
In 6ch Mode: Counter Latch 1/ch
Measurements Pulse rate measurement and pulse period measurement
Counter Input Specifications (line receiver input)
Input voltage EIA standard RS-422-A
line driver levels		 High-level input
voltage		 VIT+: 0.1 V min.
Input impedance 120 Ω ±5% Low-level input
voltage		 VIT-: -0.1 V max.
Hysteresis voltage Vhys (VIT+ - VIT-): 60 mV
Maximum response frequency In 2ch Mode: A- and B-phase: Single-phase 1 MHz (phase differential pulse input x4: 4 MHz), Z-phase: 1 MHz
In 6ch Mode: Single-phase 100 kHz
External power supply output (5 V) *1 Output voltage: 4.9 to 5.25 VDC (5 VDC +5%/-2%)
Output current: 500 mA/channel min., 1 A/unit min.
External Input Specifications
Input voltage 20.4 to 28.8 VDC
(24 VDC +20%/-15%)		 ON voltage/
ON current		 15 VDC min./3 mA min.
Input current 3.3 mA typical (24 VDC) OFF voltage/
OFF current		 5.0 VDC max./1 mA max.
ON/OFF response time 1 μs max./1 μs max.
Internal I/O common processing PNP
I/O power supply method Supply from the NX Bus
External Output Specifications
Rated voltage 5 to 24 VDC
Load voltage range 4.75 to 28.8 VDC Residual voltage 0.6 V max.
Maximum value of load current 0.5 A/point, 1.8 A/Unit Leakage current 0.1 mA max.
ON/OFF response time 1 μs max./3 μs max. (at load current 7 to 500 mA)
Internal I/O common processing PNP Load Short-circuit
Protection		 None
I/O power supply method External supply, 4.75 to 28.8 VDC
Current consumption from I/O power supply 30 mA max.
Dimensions 24 (W) × 100 (H) × 71 (D) Isolation method Photocoupler isolation
Insulation resistance 20 MΩ min. between
isolated circuits
(at 100 VDC)		 Dielectric strength 510 VAC between isolated circuits
for 1 minute at a leakage current
of 5 mA max.
NX Unit power consumption • Connected to a CPU Unit
1.45 W max.
• Connected to
Communications Coupler
Unit 1.05 W max.		 Current consumption
from I/O power supply		 Unit current consumption: 30 mA max.
External 5 V power supply
consumption: 0.25 × external 5 V
power supply current consumption *2
Weight 140 g max.
Circuit layout Count input, external input
3961_sp_5_2


External output
3961_sp_5_3
Installation orientation and restrictions Refer to NX-series High-speed Counter Units User's Manual (Man. No. W647).
Terminal connection diagram Refer to Terminal Block Arrangement and Wiring Example on Data Sheet.

*1. External power supply (5 V) may be unavailable due to installation orientation or ambient operating temperature. Refer to NX-series High-speed Counter Units User's Manual (Man. No. W647).
*2. Use this formula to convert 5 V power supply current consumption to 24 V power supply current consumption.

last update: January 5, 2026

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