GE MDI50 Digital Input Module 32-Channel Nexus Series

GE MDI50 Nexus Series Digital Input Module

Product Introduction

The GE MDI50 belongs to the Nexus series and functions as a high-density digital input module. This unit delivers 32 discrete input channels, each accepting dry contact or sink-current signals with a 48V DC query voltage. Sequence of Events (SOE) capability is built-in, providing 1ms timestamp accuracy for critical alarm and trip events. Additionally, the last four channels support pulse counting (PI) up to 1.5kHz, making the MDI50 suitable for flowmeter or encoder applications. With robust isolation, LED diagnostics, and CE compliance, this module excels in power plants, substations, and process automation systems.

Technical Specifications

Input Characteristics
The module offers 32 digital input channels arranged in a single group. Each channel accepts dry contact closure or sinking current from a field device. The query voltage is set at 48V DC, providing reliable wetting for contacts in dusty or corrosive environments. Additionally, the GE MDI50 incorporates programmable input filtering from 3ms to 50ms, with a default setting of 24ms. This filter effectively debounces mechanical contacts and rejects high-frequency noise.

SOE and Time-Stamping
Sequence of Events functionality is embedded within the MDI50 firmware. Every state change on any input channel receives a timestamp with 1ms resolution. This precision enables accurate sequence reconstruction during fault analysis, helping engineers identify the root cause of system trips. Meanwhile, the module buffers events locally to prevent data loss during bus congestion.

Pulse Input and Counting
The last four channels (29–32) support dual functionality. Beyond standard digital input, these channels operate as pulse inputs with a frequency range of 0 to 1.5kHz. The GE MDI50 accumulates pulse counts in internal registers, which the host controller reads via the serial bus. This feature eliminates the need for separate counter modules in applications like totalised flow measurement or shaft speed monitoring.

Isolation and Protection
Channel-to-ground isolation is rated at 500VAC, while the system bus isolation reaches 1500VAC. This separation protects the main controller from transient surges originating in the field wiring. Furthermore, the MDI50 includes reverse-polarity protection on each input, preventing damage from accidental miswiring.

Communication and Status Indication
The module communicates over a redundant high-speed intelligent serial bus at 1Mbps via a female DB-9 connector. Front-panel LEDs provide clear visual status: RUN indicates module health, COM shows bus activity, and FLT signals internal faults. Additionally, individual channel LEDs illuminate when the corresponding input is active, simplifying on-site troubleshooting.

Power Consumption
Typical power draw is 1.2W, with maximum consumption reaching 8.5W when all 32 channels are simultaneously active. The GE MDI50 accepts a single 24V DC supply (21.6–26.4V range), which also powers the internal isolation circuitry.

Mechanical and Environmental Parameters

Physical Dimensions
The module measures 209mm in height, 129.5mm in width, and 51mm in depth. Its compact form factor matches standard Nexus series backplanes.

Terminal Connections
A single-row European-style removable terminal block accommodates 2.5mm² wire, supporting dual-wire terminations. This detachable design simplifies field wiring and module replacement without disturbing connected cables.

Environmental Limits
Operating temperature spans 0°C to 60°C, with relative humidity between 10% and 90% (non-condensing). Vibration resistance covers 10–500Hz at acceleration not exceeding 10m/s². For dust tolerance, airborne particles larger than 0.5µm must stay below 18,000 particles per litre, ensuring reliable operation in most industrial settings.

Regulatory Compliance
The MDI50 complies with CFR 47 FCC Part 15: 2009, ANSI C63.4-2003, EN 61326-1: 2006, CISPR 11: 2007, and IEC 61000-4-2/3/4/5/6/8/11. It carries CE certification as part of the complete GE Nexus system.

Installation Guidance

Mounting Instructions
Secure the GE MDI50 to the rack using screw-type mounting. Ensure the backplane connectors align properly before tightening. Tighten screws in a cross pattern to maintain even pressure on the PCB.

Wiring Recommendations
Use 2.5mm² stranded or solid copper wire for field terminations. Strip approximately 7–8mm of insulation before inserting into the removable terminal block. For dry contact inputs, connect one side of the contact to the channel terminal and the other to the common return (48V DC minus). For sink-current devices, verify that the external power supply shares a common ground with the module.

Filter Configuration
Adjust the input filter time via configuration software. Shorter filter settings (3–10ms) suit fast digital signals, while longer settings (30–50ms) work better with mechanical switches. The default 24ms offers a balanced starting point for most applications.

Bus and Power Connection
Connect the DB-9 female port to the system bus using a shielded serial cable. Apply 24V DC power to the designated terminals. The MDI50 does not require redundant power, but a single supply must deliver at least 0.4A continuously.

Packaging List

• GE MDI50 digital input module × 1

• Removable terminal block (single-row, European-style) × 1

• Screw mounting kit (screws and washers) × 1 set

• Product label with serial number × 1

• Quick installation guide (printed) × 1

Shipping Method: FedEx, UPS, DHL

Frequently Asked Questions

Q1: Can the MDI50 capture both digital status and pulse count simultaneously on the last four channels?
No. Channels 29–32 operate in either standard digital input mode or pulse counting mode. You must select the desired function during module configuration. However, the digital state remains readable even in pulse mode.

Q2: What is the minimum pulse width required for reliable counting?
The GE MDI50 requires a pulse width of at least 333µs for reliable detection at the maximum 1.5kHz frequency. For lower frequencies, the minimum width increases proportionally with the period.

Q3: Does the module retain SOE data if the bus communication fails?
Yes. The MDI50 buffers up to 128 SOE entries locally. Once bus communication restores, the host controller retrieves all stored events. No data loss occurs during temporary network interruptions.

Q4: Can I use a 24V DC field supply instead of 48V DC?
The MDI50 is specifically designed for 48V DC query voltage. Using 24V DC may result in unreliable contact wetting, especially with oxidised or high-resistance contacts. GE recommends 48V DC for full specification compliance.

Q5: What does the SOE accuracy of 1ms refer to?
The 1ms accuracy represents the timestamp resolution relative to the module's internal clock. All channels synchronise to the system time master, ensuring consistent time-stamping across multiple modules in the same rack.