Section 5: Basic Digital Multimeter (DMM) Operation
Series 3700 System Switch/Multimeter User's Manual
5-20
3700S-900-01 Rev. C / July 2008
Speed, accuracy, and settling times for AC current and
voltage
The Series 3700 is an AC-coupled RMS meter. For an AC waveform with a DC
content, the DC component is removed before the RMS is calculated. The RMS
converter rectifies the AC waveform and creates a proportional DC level. The
amount of the DC level is dependent on input level, frequency, and
dmm.detectorbandwidth
setting.
The following example illustrates how to optimize ACV. The block diagram
shows a two-channel scan measuring 1Vrms on the first channel and
approximately 100mV on the second channel. Due to the internal DMM circuitry,
the RMS converter must settle 50ms before the start of the first reading on each
channel. For each channel, 25 readings are taken at a 1msec interval. With
Autodelay off, the measurement uncertainty follows the 50msec settling time of
the RMS converter. With Autodelay Once, the first reading is delayed 50msec,
allowing the RMS converter to settle, then 25 readings are taken at a 1msec
internal, resulting in <0.01% uncertainty.
Figure 5-12: Simplified ACV Detector Bandwidth 300 (FAST) Scan Block Diagram