Description

FOXBORO  FBM201E  Analog Input Interface module

1. Signal Acquisition
   The FBM201E receives analog signals from on-site sensors through its multi-channel input interface (usually 8 independent channels). These signals can be:

• Current signals (such as 4-20mA, 0-20mA)
• Voltage signals (such as 0-10V, ±5V, ±10V)
• Resistance signals (such as resistance changes of RTD temperature sensors)
• Special signals (such as millivolt-level temperature difference signals of thermocouples)

2. Signal Conditioning
   The collected original analog signals usually need preprocessing to meet the requirements of subsequent A/D conversion:

• Signal amplification: Adjust the gain for weak signals (such as thermocouples).
• Filtering: Remove high-frequency noise and power supply interference through hardware filters (such as RC filters, digital filters).
• Linearization processing: Perform mathematical compensation on nonlinear signals (such as the resistance-temperature curve of RTD).
• Range conversion: Normalize input signals of different ranges to the effective input range of the A/D converter.

3. A/D Conversion
   The FBM201E adopts Sigma-Delta modulation technology to achieve high-precision analog-to-digital conversion:

• Oversampling: Sample at a rate much higher than the Nyquist frequency to reduce quantization noise.
• Digital filtering: Improve the effective number of bits (usually 16-24 bits) through a digital decimation filter.
• Integration period: Configurable integration time (such as 20ms corresponding to 50Hz power frequency suppression) to eliminate power frequency interference.
• Conversion accuracy: The typical accuracy is ±0.03% FS (full scale), and the temperature coefficient is as low as ±50ppm/°C.

4. Digital Signal Processing
   The converted digital signals are processed by the internal processor of the module as follows:

• Calibration compensation: Apply factory calibration parameters to correct zero, range, and linear errors.
• Alarm judgment: Compare the measured value with the preset high and low limit thresholds in real time to trigger alarm output.
• Rate of change limitation: Suppress sudden change signals to prevent misoperation caused by interference.
• Data formatting: Convert the original values into engineering units (such as °C, MPa, m³/h).

5. Communication and Integration
   The processed data is transmitted to the DCS controller through fieldbus protocols (such as FOXBORO’s I/A Series system bus):

• Redundant communication: Supports dual redundant buses to ensure the reliability of data transmission.
• Status feedback: The module uploads its working status in real time (such as power failure, channel abnormality).
• Remote configuration: Sampling rate, filtering parameters and other configurations can be modified remotely through upper computer software.

6. Power Supply and Safety Mechanism

• Isolated power supply: The module uses an isolated DC/DC converter internally to ensure the separation of power supply and signal ground.
• Overvoltage/overcurrent protection: Each channel has a built-in current-limiting resistor and TVS (transient voltage suppressor diode) to prevent damage from surges.
• Fail-safe design: When a power failure or communication interruption is detected, the module can output a safe value according to a preset strategy (such as maintaining the last value, outputting an alarm value).

• Temperature/pressure monitoring: Connecting thermocouples, RTDs or pressure transmitters.
• Flow/liquid level measurement: Collecting signals from flowmeters or liquid level meters with 4-20mA output.
• Environmental parameter monitoring: Such as the acquisition of sensor signals like pH value and conductivity.