Measurement Computing DBK Part 2 User Manual
Page 147
Three examples of using the excitation source follow. They are Position Sensing, Resistance/Thermistor
Measurement, and Reading a Transducer.
Source Impedance and Settling Time
High speed multiplexing of signal sources with non-zero impedance will result in reading errors caused by
settling time. In the simplest form, a multiplexing system consists of a group of switches, with internal
resistance, and an output capacitance at the input of an amplifier feeding an A/D converter with a sample-
hold circuit on the input. During the short time a channel signal is connected to the A/D amplifier, the
signal must charge the output capacitance to the true value of the signal so that the sample-hold captures an
accurate value for the A/D converter to digitize. If the source has significant internal impedance the
voltage reading will be reduced.
DBK Option Cards and Modules
989494
DBK80 pg. 3