1. digital data acquisition1 Measuring ? „Wer misst, misst Mist.“ numeric result Sensing, Signal Processing Evaluation Physical/Chemical Property Physical/Chemical Property Measurement numeric result DIGITAL RESULT numeric result DIGITAL RESULT Digitizing in analogue measurements Digitizing in a digital measurement 5,53 5,53

2. digital data acquisition2 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.

3. digital data acquisition3 Analogue/Digital Converter MUX PGA A/DC analogue signal(s) S/H t 0 programming input selection of signal source and amplification settling time 10 to 100 µs Start conversion “polling” sample 1 to 5 µs hold - A/D conversion 10 to 30 µs digital data integration time  measurement cycle  t

4. digital data acquisition4.. or using VCO A Voltage Controlled Oscillator (VCO), also called Voltage to Frequency Converter (V/FC) converts an input voltage V in into an oscillating TTL-signal with the frequency f out proportional to V in. t 0 VCO V in digital counter counting time, gate time µs to s-range digital data counter reset and start commandcounter stop command measurement cycle  t integration time  =  t

5. digital data acquisition5 Registering Digital Data tt analogue signal digital readout tt analogue signal digital readout VCO averaging PGA-settlingSAMPLEA/D conversion