Technical Specifications

FAQ

1. What is the primary function of the 3701/55 Emergency Shutdown Device?

The 3701/55 ADAPT Emergency Shutdown Device is a standalone safety PLC designed to provide emergency shutdown and overspeed protection for rotating machinery. It is intended for applications such as steam turbines, gas turbines, hydro turbines, expanders, and other process equipment where rapid and dependable shutdown is required. The system combines programmable safety logic with integrated overspeed detection, allowing speed signals, discrete inputs, and process variables to be evaluated together. When a configured trip condition is detected, the system can activate its relay outputs to initiate the appropriate machinery shutdown sequence.

2. How does the triple-modular-redundant architecture of the 3701/55 work?

The 3701/55 uses three CPU processing modules to implement triple modular redundancy. Each CPU module processes two independent speed input channels, providing six speed channels across the system. The redundant architecture allows the system to compare processing results and maintain reliable protection logic even when an individual processing path experiences a fault. This design is particularly important for safety-critical machinery because it helps reduce the possibility of a single internal failure causing an incorrect shutdown decision or preventing the system from responding to a genuine dangerous condition.

3. How many speed and process inputs does the 3701/55 support?

The 3701/55 provides six speed input channels through its three redundant CPU processing paths. In addition, the system monitors an array of 32 discrete and process-variable inputs. Twelve channels within this input array can be configured as either discrete inputs or 4–20 mA analog inputs, while the remaining channels are reserved for discrete input functions. This flexible input structure allows the ESD system to monitor overspeed signals together with trip switches, process conditions, permissive signals, and other safety-related field inputs.

4. What is the speed measurement range of the 3701/55?

The 3701/55 supports overspeed monitoring from 1 to 999 events per revolution and provides a maximum full-scale speed range of 120,000 rpm. Proximity speed inputs operate from 3 Hz to 10 kHz, while magnetic pickup inputs support an operating frequency range of 2 Hz to 20 kHz. The proximity input requires a minimum pulse amplitude of 1.0 Vpp and supports up to 24 Vpp. Magnetic pickup inputs can accept up to 80 Vrms. These input characteristics allow the system to accommodate different speed sensor technologies used on industrial rotating machinery.

5. What communication capabilities are available on the 3701/55?

The 3701/55 provides six Ethernet ports with 10/100 Mbps communication capability. It uses TCP/IP and supports both DHCP and static IP addressing, allowing the system to be integrated into a plant network or a dedicated machinery protection network. Network configuration modifications are password protected, helping prevent unauthorized changes to critical protection settings. NTP time synchronization is also supported, which can be useful when correlating shutdown events, alarms, and other machinery protection records with information from other plant systems.

6. What type of relay outputs does the 3701/55 provide?

The 3701/55 uses SPDT relay outputs for machinery shutdown functions. The relay contacts are rated up to 5 A at 250 VAC with a maximum of 1500 VA, or 5 A at 250 VDC with a maximum of 150 VA. Depending on the relay channel configuration, voting logic can be configured for independent 1oo1 operation or TMR 2oo3 voting. The trip action can also be configured for energized or de-energized operation. This flexibility allows the shutdown logic to be adapted to different turbine and process equipment control schemes while supporting fail-safe design requirements.

7. What power supply and environmental conditions are required for the 3701/55?

The 3701/55 operates from an 18–36 VDC power supply. Typical power consumption is approximately 24 W, with a maximum specified consumption of 35 W. The normal operating temperature range is -30°C to +65°C, while the storage temperature range is -40°C to +85°C. For hazardous-area installations, the power supply and associated installation must meet the applicable local certification requirements. Proper grounding, wiring, and power protection are important because the ESD is part of a safety-critical machinery protection system.

8. What should be checked if the 3701/55 does not initiate a shutdown when expected?

Troubleshooting should begin by checking the active trip logic and the status of the relevant speed, discrete, and analog inputs. For overspeed protection, verify that the speed sensor is producing a signal within the required voltage and frequency range and that the sensor wiring is correctly connected. The status of the three redundant processing paths should also be reviewed for diagnostic faults. Next, check the configured voting logic, relay status, trip thresholds, and system configuration using the appropriate Bently Nevada configuration software. If the logic is operating correctly but the external equipment does not respond, inspect the relay wiring and downstream shutdown circuit. Because the 3701/55 performs a safety-critical function, any suspected protection fault should be investigated systematically rather than bypassing the configured trip logic.