ARM55T

The Yokogawa ARM55T is a 32-point mechanical relay board designed for wet-contact digital output applications in the Fieldnetwork I/O (FIO) subsystem of the CENTUM VP control system. It interfaces with digital output modules and field devices, providing relay-based switching with individual AUTO/OFF/ON selection for each output point. The board supports single or dual-redundant configurations.

Relay Output Function and Switching Control

The ARM55T receives output signals from a Yokogawa digital output module and switches external field-device circuits through mechanical relays. Unlike the ARM55D dry-contact version, the ARM55T provides wet-contact outputs with externally supplied field power.

Each of its 32 output points has an AUTO/OFF/ON switch:

• AUTO: Output operation follows the control signal from the digital output module.
• OFF: Forces the corresponding output to the OFF state.
• ON: Forces the corresponding output to the ON state.

This individual switching arrangement allows local output-state selection without changing the controller's output configuration.

Electrical Ratings and Field Connections

The ARM55T supports 32 output points with M4 screw terminals for field-device connections. Its wet-contact outputs are divided into two groups, channels 1-16 and 17-32, with separate field power supply connections.

The maximum load rating depends on the supply type:

• 250 V AC: 0.6 A per point
• 30 V DC: 0.6 A per point
• 125 V DC: 0.1 A per point

The external field-device power supply supports a dual-line arrangement, with power supplied separately for each 16-point group. The maximum current per line is 9.6 A at 250 V AC or 30 V DC, and 1.6 A at 125 V DC.

Compatible I/O Modules and Signal Cables

The manufacturer specifies the ARM55T for use with the ADV551 32-point digital output module and the ADV561 64-point digital output module. The ATD5A terminal block is specified for the ADV551 configuration.

The corresponding signal cables are:

• AKB331 for 32-point connections.
• AKB337 for 64-point connections.

When using one ADV561 module, two relay boards and two AKB337 signal cables are required. This arrangement distributes the 64 output points across two 32-point relay boards.

Technical Specifications

Parameter	Specification
Model	ARM55T
Brand	Yokogawa
Product Type	Mechanical Relay Board
Relay Type	Mechanical Relay
Output Type	Wet Contact Output
Number of Output Points	32
Output Selection	AUTO/OFF/ON
Maximum Load	250 V AC: 0.6 A per point
Maximum Load	30 V DC: 0.6 A per point
Maximum Load	125 V DC: 0.1 A per point
Minimum Load	5 V, 10 mA
Internal Circuit Power Supply	24 V DC
Internal Circuit Current Consumption	Max. 0.65 A
Field Power Supply	Dual-line, per 16 points
Field Power Supply Capacity	250 V AC / 30 V DC: Max. 9.6 A per line
Field Power Supply Capacity	125 V DC: Max. 1.6 A per line
Field Connection Terminals	M4 screws
Compatible I/O Modules	ADV551, ADV561
Terminal Block	ATD5A (for ADV551 configuration)
Signal Cables	AKB331, AKB337
Insulation Resistance	At least 10 MOhm at 500 V DC
Withstanding Voltage	Field terminals to case: 3 kV AC for 1 minute
Withstanding Voltage	24 V power terminals to case: 500 V AC for 1 minute
Withstanding Voltage	24 V power terminals to field terminals: 3 kV AC for 1 minute
Operating Temperature	0 to 50 deg C
Ambient Humidity	10 to 90% RH
Weight	2.6 kg

Field Installation and Load Protection

When switching inductive loads, Yokogawa specifies an external protection circuit connected in parallel with the load to suppress switching noise. Use an RC circuit for AC loads and a diode for DC loads.

The field-device power supply and internal 24 V DC circuit supply serve different functions. Both external supply requirements must be considered when planning the relay board wiring.

Frequently Asked Questions

Q: What is the difference between the ARM55T and ARM55W?

A: Both models provide 32-point mechanical wet-contact outputs and support single or dual-redundant configurations. The ARM55T additionally provides individual AUTO/OFF/ON switches for output selection, while the ARM55W does not have these switches.

Q: Which Yokogawa digital output modules can be connected to the ARM55T?

A: The specified modules are ADV551 and ADV561. The ADV551 uses the ATD5A terminal block, while the ADV561 uses the AKB337 signal cable arrangement with two relay boards for its 64 output points.

Q: What should be checked when selecting the ARM55T for field-device control?

A: Check the output voltage, current per point, total field power supply capacity, and minimum load requirements. For inductive loads, provide the specified parallel protection circuit. The maximum load ratings must be observed for the corresponding AC or DC supply condition.

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