Yokogawa YS1700-020/A31 | Programmable Single-Loop Controller

• Model: YS1700-020/A31
• Brand: Yokogawa
• Series: YS1000
• Core Function: Executes programmable single-loop process control
• Type: Programmable indicating controller
• Key Specs: 24–120 VDC / 100–120 VAC supply; RS-485; Modbus/YS/PC-link protocols
• Status: Discontinued; legacy replacement stock should be verified

Product Introduction

Yokogawa YS1700-020/A31 is a programmable indicating controller for single-loop process control, combining local indication, control functions, and serial communication in one panel-mounted instrument. The YS1700 platform supports user programming and is intended for process applications such as boilers, chemical systems, utilities, and plant instrumentation.

The /A31 option is important here: it provides RS-485 communication supporting PC-link, Modbus, YS protocol, and peer-to-peer communication. Yokogawa also specifies this option for direct communication with CENTUM CS3000/VP through the applicable interface architecture.

Key Technical Specifications

The exact input configuration should be checked against the complete suffix code and original nameplate. Yokogawa’s model-selection documentation shows that direct-input options such as thermocouple, RTD, mV, potentiometer, and transmitter inputs are separately specified.

Yokogawa YS1700-020/A31

Application and Selection Notes

This controller fits plants that need a local PID loop with programmable logic and serial integration. Boiler control is one documented example, while chemical dosing and other process-control duties are also supported by Yokogawa’s application material.

For replacement purchasing, do not match only the front-panel appearance. Confirm the input option, power-supply code, communication option, control program, and existing wiring. The /A31 suffix specifically identifies the RS-485 communication configuration.

Because the model is discontinued, it is more appropriate for maintaining an installed system than specifying a new control platform. Yokogawa provides YS1000 replacement documentation for migration from older controllers, so a planned modernization can be evaluated separately.

Quality Inspection and Shipping

A practical spare-parts inspection sequence is:

1. Incoming inspection: Verify model code, serial number, display, terminals, housing, and manufacturer markings.
2. Live Test: Power the controller with a suitable regulated supply and verify startup, display, keypad, alarms, and controller operation.
3. Communication Test: Check the RS-485 interface and, where available, verify Modbus or YS protocol communication.
4. Configuration Verification: Record input configuration, communication parameters, firmware/software information, and user-program settings.
5. Final QC: Complete the Test Report, photograph the unit, protect the terminals and display, and use ESD-safe packaging.

For export orders, the commercial invoice should state the actual product description, country of origin, quantity, and transaction value. Customs classification should be checked against the final configuration and destination-country requirements.

Common Replacement Pitfalls

Input-option mismatch: A YS1700 with a different input option may not accept the same field signal. Check the complete model code.

RS-485 settings: Baud rate, address, parity, and termination must match the host system. The manual specifies an internal 120 Ω terminating resistor that can be enabled at the end of an RS-485 network.

Program transfer: The controller’s user program is part of the application. Preserve the original configuration before replacement.

Power variation: Confirm whether the installed cabinet supplies AC or DC before energizing the spare.

System migration: If replacing an older YS170 or SLPC, Yokogawa provides dedicated conversion guidance through YSS1000 software.

Personally, I would photograph the complete nameplate before ordering. With Yokogawa controllers, one small suffix can change the communication or input configuration—and that is exactly the sort of detail that causes an avoidable commissioning delay.

Quick Conclusion

• Programmable single-loop process controller
• YS1000-series architecture
• /A31 provides RS-485 communication
• Supports Modbus, PC-link, YS protocol, and peer-to-peer communication
• Suitable for legacy process-control and DCS interface applications
• Discontinued model; verify exact input, power, communication, and program configuration before purchase