Issue link: https://resources.mouser.com/i/1442820
| 22 | Recommendations for Signal Processing A typical current source module block diagram is shown in Figure 2 and was built to evaluate the accuracy of a shunt based current measurement system. The module consists of an Analog Front End (AFE) with a current sense amplifier with analog buffer, 24 bit ADC and SPI interface. Bourns has built a module for evaluation of the shunt and tested the CSM2F-8518 shunt (100µΩ nominal resistance) as shown in Figure 2. A single board microcontroller kit is programmed to communicate with the module over an SPI connection. The current for the measurement was generated using a precision current source. The resistance of the shunt is, first of all, determined using the known current from the current source and a precision 4-wire voltmeter. Once the actual resistance of the shunt has been measured we can record the voltage across the shunt using the current sense module and compare it with what we were expecting given the actual resistance value. The current sense amplifier has a common mode voltage of 80V maximum allowing for the module to be placed at the high end in 48V battery systems. The module also contains a surface mount temperature sensor with a PWM output proportional to the ambient temperature. Figure 3 shows the temperature sensor output at room temperature. The amplifier power is supplied by a DC supply of +5V. The power in this experiment comes from an LDO with the original supply coming from the USB interface. For an isolated 5V supply a low power micro-converter (Flyback or push-pull) can provide the necessary isolation with the required safety level. Figure 4 shows the data points collected from the A/D input terminals with an average of 22.44364mV and peak to peak variation of 0.007mV over the sampling period. Part Three The accuracy of the measurements can be calculated using the following formula at room temperature The accuracy is (Expected Voltage-Actual Measurement) mV*100 Full Range of Op Amp Figure 3: Data in Degrees Celsius Recorded by the Module Figure 4: Data in Millivolts Recorded by the Current Sense Module