Measuring ?

1. Measuring ? „Wer misst, misst Mist.“ Digitizing in analogue measurements Physical/Chemical Property Measurement Sensing, Signal Processing Evaluation 5,53 numeric result numeric result DIGITAL RESULT Digitizing in a digital measurement digital data acquisition

2. The Analogue//Digital Interface Digital circuits for the analogue//digital interface are typically realised in TTL components and operational amplifiers working with 3 to 5 V DC and currents up to 20mA. State of the art instruments are mostly based on commercial PC compatible computer components. Add on components are available to make a standard PC a digital recording instrument for analogue data. A single bit on a digital output can directly be utilised as switch Digital words can be converted into analogue output signals via a D/AC Analogue values can be converted into digital words using a D/AC and a comparator in a trial and error process (A/DC). The analogue to digital conversion is thus a more complex and time consuming process than a comparable D/AC step. digital data acquisition

3. MUX PGA Analogue/Digital Converter programming input selection of signal source and amplification Start conversion “polling” S/H A/DC digital data analogue signal(s) measurement cycle Dt hold - A/D conversion 10 to 30 µs settling time 10 to 100 µs sample 1 to 5 µs integration time t t 0 digital data acquisition

4. A Voltage Controlled Oscillator (VCO), also called Voltage to Frequency Converter (V/FC) converts an input voltage Vin into an oscillating TTL-signal with the frequency fout proportional to Vin. counter reset and start command counter stop command t 0 .. or using VCO digital data digitalcounter VCO Vin measurement cycle Dt counting time, gate time µs to s-range integration time t=Dt digital data acquisition

5. analogue signal analogue signal digital readout digital readout Dt Dt Registering Digital Data A/D conversion PGA-settling SAMPLE VCO averaging digital data acquisition