Model SR715 Model SR720 LCR Meters

OPERATIONcapacitors (test voltage = 0.5 Vrms). In these cases, use the vernier setting toobtain the exact voltage required. In general use the largest voltage possible forthe best signal to noise ratio and accuracy.RANGEThe SR715/720 has 4 measurement ranges (0-3). The range may be selectedmanually or the unit can autorange. The table below specifies the impedanceranges for each of the measurement ranges. Each of the four ranges has sourceimpedance of approximately the mid-scale impedance. Note that themeasurement ranges determine an impedance range (not a value range), so theranges of inductance and capacitance depend upon the test frequency. Theparameter f is the test frequency. In addition, the impedance of capacitors isinversely proportional to its capacitance, so larger capacitors are measured in thelower impedance ranges.Measurement Range and Impedance RangeMeasRange Source R Resistance Inductance Capacitance3 25.0 Ω 10 µΩ - 0.0001 µH - 99999 µF -100 Ω 15.9/f H 1.59/f mF2 400 Ω 100.0 µΩ - 15.9/f H - 1.59/f mF -1.6 kΩ 256/f H 99.5/f µF1 6.4 K Ω 1.6 kΩ - 256/f H - 99.5/f µF -25.6 kΩ 4074/f H 6.22/f µF0 100 K Ω 25.6 kΩ - 4074/f H - 6.22/f µF -2000 MΩ 99999H 0.00001 pFF is testfrequencyAUTORANGINGDuring normal operations the unit automatically changes to the most accuraterange for the device under test. When the unit measures an impedance that isout of its current range, it goes up or down one range, and makes anothermeasurement. If this measurement is within the current range it displays it; If not,it changes ranges (if available), and repeats this process. There is built inhysteresis to avoid repeated range changes when a component is on a rangeboundary. Up range changes occur when the impedance measured exceeds450% of the midscale impedance (i.e. the source impedance), or 12.5% over thenominal range limit. Down range changes occur when the measured impedancedrops below 22% of the midscale impedance, or 12.5% below the nominal range.See the table below for the actual values where the range changes occur.Range Change Points When AutorangingRanging To Lower Impedances Ranging To Higher ImpedancesRange Change Impledance Range Change Impledance2 to 3 Z < 88 Ω 3 to 2 Z > 115 Ω1 to 2 Z 1.8 kΩ0 to 1 Z < 22.4 kΩ 1 to 0 Z > 29.9 kΩRANGE HOLDIt is sometimes desirable to disable autoranging since it takes nearly a completemeasurement cycle each time a range changes occurs. This can be annoying ifthere are no parts in the fixture and the unit is continuously triggering, since anempty fixture appears as a very large (nearly infinite) impedance. The unit will2-6