NFAF135-S50

The Yokogawa NFAF135-S50 is identified as a frequency input module for industrial control system applications. It is intended for frequency-signal acquisition, where input signals are processed for use by the control system. The exact input range, channel configuration, signal characteristics, and hardware compatibility should be confirmed against the applicable NFAF135-S50 documentation before selecting a replacement or configuring a system.

Frequency Measurement and Signal Processing

The module measures the time intervals between incoming pulses and calculates their corresponding frequency. Its measurement circuit uses pulse-edge detection and interval timing, while the internal processor performs the frequency calculation. This allows the controller to obtain frequency or rotational-speed process values rather than simply counting input pulses.

Input Channels and Signal Types

The NFAF135 provides eight individually isolated input channels. It accepts the following signal types:

• Dry-contact pulse input using an open-collector contact.
• Dry-contact pulse input using a relay contact.
• Voltage pulse input using a rectangular waveform.

The input mode determines the terminal connections and associated configuration settings. For open-collector contact inputs, the maximum input frequency is limited to 800 Hz; the general 10 kHz rating should not be applied indiscriminately to every input mode.

Measurement Performance

The module covers an input frequency range of 0.1 Hz to 10 kHz, with a frequency accuracy of 0.1% of reading and a 10 ms data update cycle. The wide measurement range supports both low-speed rotational monitoring and higher-frequency pulse measurements.

Parameter Table

Parameter	Specification
Model	NFAF135-S50
Brand	Yokogawa
Product Type	Frequency Input Module
Number of Input Channels	8
Channel Isolation	Individually isolated
Input Signal Types	Dry-contact pulse, voltage pulse
Input Frequency Range	0.1 Hz to 10 kHz
Maximum Frequency - Open-Collector Input	800 Hz
Frequency Accuracy	0.1% of reading
Data Update Cycle	10 ms
Minimum Input Pulse Width	40 us
Voltage Pulse Swing	3 V or more
Voltage Pulse High Level	3 to 24 VDC
Voltage Pulse Low Level	-1 to 8 VDC
Signal Source Resistance	1 kOhm or less
Contact Input Open Resistance	100 kOhm or more
Contact Input Closed Resistance	200 Ohm or less
Transmitter Power Supply	Selectable 12 VDC / 24 VDC
Withstanding Voltage	500 VAC for 1 minute, input-to-system and channel-to-channel

Configuration and Connection Requirements

Three input modes are documented, and each requires the corresponding terminal arrangement and configuration:

• Open-collector contact: Uses INB-INC connections. The transmitter supply and shunt-resistance settings must match the field circuit.
• Relay contact: Uses INA-INB connections. This mode has a different transmitter-supply and resistance configuration from the open-collector mode.
• Voltage pulse: Uses INB-INC connections and requires the input voltage levels to remain within the specified signal limits.

The module's transmitter supply and input-mode settings are configured through the STARDOM Resource Configurator. The available 12 VDC or 24 VDC supply selection should be checked against the connected sensor's electrical requirements.

Frequently Asked Questions

Q: Can the NFAF135-S50 accept both contact pulses and voltage pulses?

A: Yes. It supports open-collector contact pulses, relay contact pulses, and rectangular voltage pulses. The selected input mode determines the wiring and configuration requirements.

Q: Can all eight channels measure frequencies up to 10 kHz?

A: The general input frequency range is 0.1 Hz to 10 kHz. However, open-collector contact input is limited to 800 Hz, so the actual operating range depends on the selected input mode.

Q: What should be checked when replacing an existing NFAF135 module?

A: Verify the complete ordering code, input signal type, channel wiring, transmitter supply setting, and controller/base-module compatibility. The model designation alone is insufficient to establish that every configuration is interchangeable.

Ordering Code and Configuration Notes

Yokogawa's product selection documentation lists NFAF135 configurations with the S50 specification code, followed by additional option codes such as 13S00, 13S10, and CCC01. Therefore, NFAF135-S50 may not represent the complete ordering code. Confirm the remaining suffix and connector configuration against the equipment nameplate before ordering. 

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