RickS, DaveB, TonyS, FranciscoL

On Friday, March 22, we measured an SRS SR340 function generator (FG) using three Keithley digital multimeters (KVM) to calculate the latency between each KVM. The FG was configured to make a ramp/sawtooth wave set to 20 Vpp at 0.1 Hz. The KVMs were configured to read 200 samples without delay. Figure "...200samples.pdf" shows the raw data from the KVM. Figure "...samples_zoom.pdf" is zoomed in the first section with a line fitted to the data. The line has a slope of m = 2 V/s.

The differences from the first KVM (id: 8019157) to the second KVM (id: 8018958) is plotted in blue on figure "...samples_diff.pdf" and yields a mean of 40.4 mV with a standard dev. of 0.21 mV. The differences from the first KVM to the third KVM (id: 1148559) is plotted in red on figure "...samples_diff.pdf" and yields a mean of 0.0808 V with a standard dev. of 0.44 mV. Figure "...samples_diffsub.pdf" plots each voltage difference individually. These values yield a latency between KVMs of 20.2 ms and 40.4 ms, respectively. To calculate the overall timing of the loop that stores the data, we measured the difference between a KVM 8019157 with itself (current - previous) and got a mean value of 0.1212 V, as indicated by figure "samples_diff2.pdf". The total latency of three keithleys for this measurement is of 60.6 ms.

The data shows that there is a latency of 20.2 ms between each KVM. It is safe to assume that, to sample 4 keithleys simultaneously, there will be an overall latency of 81 ms (~ 12 Hz). This latency is well within our design limits of measuring at a sample rate of 5 times per second.