Industrial Sensor Interface Solution

This industrial sensor interface solution supports multiple sensor types including strain gauges and load cells (using ACM8221 instrumentation amplifiers), thermocouples (types K, J, T, E, N, S, R, B with cold junction compensation), RTDs (Pt100, Pt1000 with 2, 3, or 4-wire configurations using ACM5320), and voltage-output sensors (0-10V, +/-10V). The flexible architecture allows mixing different sensor types on the same platform. Each input channel can be independently configured for the specific sensor type through software. The 24-bit ADC provides sufficient resolution for all common industrial sensors, while the programmable gain amplifiers optimize signal levels for each sensor's output range.

Contact our FAE team with your specific sensor requirements for a customized channel configuration recommendation.

Minimizing noise in long cable runs requires a multi-layered approach. First, use shielded twisted-pair cable for all sensor connections - the twisting reduces magnetic interference while the shield blocks electric fields. Connect the shield to ground at the receiver end only to avoid ground loops. Second, implement differential signal transmission using the instrumentation amplifier's differential inputs - this rejects common-mode noise picked up equally on both wires. Third, add RC filters (1kΩ + 100nF) at the amplifier inputs to limit bandwidth and remove high-frequency noise. Fourth, use the ACM2420's 50/60 Hz rejection feature to eliminate power line interference. Fifth, ensure proper grounding - use a star ground configuration with analog and digital grounds connected at a single point. For extremely noisy environments, consider the isolated version using ACM1050 transceivers.

Use shielded twisted-pair cable, differential inputs, input filtering, and proper grounding for best noise immunity.

The recommended calibration procedure involves three steps: zero calibration, span calibration, and linearity verification. For zero calibration, disconnect the sensor or apply zero input (shorted inputs for voltage measurements, 0°C reference for thermocouples), then record the offset and subtract it from subsequent readings. For span calibration, apply a known full-scale input (precision voltage source or calibrated weight for load cells) and adjust the gain coefficient to match the expected output. For RTDs, use precision resistance standards. For linearity verification, apply inputs at 25%, 50%, and 75% of full scale and verify errors are within specification. The ratiometric measurement architecture minimizes drift, but I recommend recalibration every 6-12 months for critical applications. The system supports both manual calibration through software commands and automated calibration sequences.

Perform zero and span calibration at commissioning. Verify linearity at multiple points. Recalibrate every 6-12 months.

The standard configuration can achieve SIL2 with appropriate architectural measures including dual-redundant channels, diagnostic coverage, and proof testing. For SIL2, implement dual-channel architecture with comparison diagnostics - if the two channels disagree beyond a threshold, the system enters a safe state. Include diagnostic checks for power supply monitoring, communication integrity, and ADC self-tests. For SIL3, additional measures are required including diverse technology (using different ADC architectures), increased diagnostic coverage (>99%), and more frequent proof testing. AcelaMicro can provide reference designs and safety manuals for SIL-rated implementations. Contact our FAE team for detailed safety architecture recommendations and documentation support.

SIL2 achievable with dual channels and diagnostics. SIL3 requires diverse technology and higher diagnostic coverage. Contact FAE for safety documentation.

The standard solution implements Modbus RTU protocol over RS-485, which is the most widely used industrial communication standard. Modbus RTU provides reliable master-slave communication with CRC error checking. The system supports function codes 03 (read holding registers), 04 (read input registers), 06 (write single register), and 16 (write multiple registers). Each sensor channel maps to specific register addresses for easy PLC integration. For CAN-based systems, the ACM1050 isolated CAN transceiver supports standard CAN 2.0B protocol with device-specific CANopen or J1939 protocol stacks available. Custom protocols can be implemented on the STM32F407 microcontroller. Ethernet connectivity can be added using external Ethernet modules for integration with modern IIoT systems.

Modbus RTU over RS-485 is standard. CANopen and Ethernet options available. Custom protocols supported on request.