AI845 Analog Input Module, Single or Redundant

Description

The AI845 Analog Input Module is designed for single or redundant applications, providing 8 channels that can be either voltage or current inputs when using MTU TU844 or TU845. For other MTUs, all channels become either voltage or current inputs.

The voltage and current inputs can withstand an overvoltage or undervoltage of at least 11 V d.c. The input resistance is greater than 10 MΩ for voltage input and 250 Ω for current input.

The module distributes the external HART compatible transmitter supply to each channel, facilitating simple connections to 2-wire or 3-wire transmitters. The transmitter power is supervised and current-limited. If an external power supply is used for HART transmitters, it must be HART compatible.

Features

• 8 channels for 0...20 mA, 4...20 mA, 0...5 V or 1...5 V d.c., single-ended unipolar inputs.
• Single or redundant operation.
• 1 group of 8 channels isolated from ground.
• 12-bit resolution.
• Current limited transmitter supply per channel.
• Advanced on-board diagnostics.
• HART pass-through communication.

The module performs cyclic self-diagnostics covering:

• External power supply, Transmitter power, and External shunt error (reported as External channel error).
• Low Pass Filter, Multiplexer, and Test channels (reported as Internal channel error).
• Analog Read Back, Reference Voltage, Internal Power Supply, Checksum, Watchdog, and Memory (reported as Module Error).

All eight channels are isolated from the ModuleBus in one group, with power to the input stages converted from the 24 V on the ModuleBus. The module supports HART pass-through functionality, but only point-to-point communication.

Various MTUs can be used:

• Single applications: TU830/TU833 (three-wire connection without additional terminals), TU810/TU814 (requires external terminals for 24 V power supply distribution), TU835/TU838 (includes a fuse per channel), TU812 (D-Sub 25 pin connector), and TU818 (connection to 2-wire sensors).
• Redundant applications: TU844/TU845/TU854 (allow mixing voltage and current inputs).

Shielded field cables are required for process connections if HART is used. The Shunt mode should be set to External shunt when using MTU TU844/TU845/TU854 or when voltage inputs are required.

Technical Data

General Specifications at 25°C

• Number of channels: 8
• Type of input: Unipolar single-ended
• Measurement range: 0...20 mA, 0...5 V, 4...20 mA, 1...5V
• Over range: +15%
• Input impedance:
  • Voltage input: 10 MΩ
  • Current input (including PTC): 250 Ω
• Maximum field cable length: 600 meters (656 yd.)
• Voltage input, maximum non-destructive: 11 V d.c.
• NMRR, 50 Hz, 60 Hz: >40 dB
• Error: Max. 0.1%
• Resolution: 12-bit
• Temperature drift: Max. 50 ppm/°C
• Update cycle time: 10 ms
• Current consumption:
  • 24 V (Modulebus): 50 mA
  • 5 V (Modulebus): 100 mA
  • 24 V (process power supply, UPx): 339 mA (max) (22 mA + transmitter current*1.32)
• Power dissipation: 3.5 W
• Transmitter supply (per channel):
  • Voltage: 24 V @ 23 mA
  • Current: 30 mA
• Supervision:
  • Module error: Analog read back, reference voltage, internal power supply, checksum, watchdog, and memory error
  • Internal channel error: Low pass filter, multiplexer, and test channels error
  • External channel error: External power supply low, transmitter power, and external shunt error
• Input filter (rise time 0-90%): 290 ms
• Isolation: Groupwise isolated from ground

Module Termination Units

• TU810, TU812, TU814, TU818, TU830, TU833, TU835, TU838, TU844, TU845, TU854

MTU Keying Code

• CC

Rated Insulation Voltage

• 50 V

Dielectric Test Voltage

• 500 V a.c.