AcelaMicro Sensor Interface

An instrumentation amplifier (INA) is a differential amplifier with high input impedance and excellent CMRR, designed for amplifying small differential signals from sensors like strain gauges and load cells. You need an INA when measuring small differential signals (mV range) in the presence of large common-mode voltages or noise. The ACM8221 provides 120dB CMRR and programmable gain from 1 to 1000.

Use an INA for amplifying small differential sensor signals in noisy environments.

RTD conditioning requires excitation current, lead wire compensation, and linearization. The ACM5320 integrates all these functions. It provides programmable excitation current (100μA or 200μA), supports 2/3/4-wire configurations for lead resistance compensation, and includes internal linearization tables for Pt100 and Pt1000 RTDs. The ratiometric measurement architecture eliminates errors from excitation current variations.

Use ACM5320 for complete RTD signal conditioning with integrated linearization.

CMRR (Common-Mode Rejection Ratio) measures how well an amplifier rejects signals that appear equally on both inputs (common-mode signals) while amplifying the difference between inputs (differential signals). High CMRR is critical for sensor applications because sensor cables often pick up noise (power line interference, EMI) that appears as common-mode signals. The ACM8221 offers 120dB CMRR, meaning common-mode noise is rejected by a factor of 1,000,000. This allows accurate measurement of small sensor signals (mV level) even in noisy industrial environments.

Select amplifiers with CMRR >100dB for industrial sensor applications with long cables.

Gain selection balances signal amplitude with bandwidth and noise. Calculate required gain as: Gain = Desired Output Range / Sensor Output Range. For example, a load cell with 2mV/V sensitivity at 5V excitation produces 10mV full scale. To utilize a 5V ADC range, need Gain = 5V / 10mV = 500. Consider noise: higher gain amplifies noise along with signal. Consider bandwidth: gain-bandwidth product is constant, so higher gain reduces bandwidth. The ACM8221 provides gain from 1 to 1000. Use the lowest gain that provides adequate signal amplitude for your ADC.

Calculate gain based on sensor output and ADC range. Use lowest gain that provides adequate signal.

2-wire RTD is simplest but includes lead wire resistance in measurement, causing errors. Use only for short leads where resistance is negligible. 3-wire RTD is most common - uses three wires of equal length and gauge. The measurement circuit compensates for lead resistance by measuring voltage drop in one lead and subtracting it. 4-wire RTD (Kelvin connection) is most accurate - uses separate pairs for excitation current and voltage measurement, completely eliminating lead resistance effects. The ACM5320 supports all three configurations, with 4-wire providing best accuracy for precision applications.

Use 2-wire for short leads only. Use 3-wire for most applications. Use 4-wire for highest accuracy.