Section 8: Theory of operation Series 3700A System Switch/Multimeter Reference Manual8-16 3700AS-901-01 Rev. D/June 2018dmm.opendetector open voltageWith dmm.opendetector = dmm.ON, a separate -1.5 A IOPENLEAD SHI and a separate SLO currentsource will pulse on and off before the start of each measurement while ISOUR remains enabled. TheA/D will monitor SHI for 2 ms, then switch to SLO for an additional 2 ms. During either phase, if theinput voltage exceeds the above table, the A/D will stop in less than 100 μs and return an overflowreading. If there are no open leads detected during the IOPENLEAD phase, the IOPENLEAD is disabled andstandard 4-wire is enabled.VMEAS with open input:If Sense HI is disconnected, VMEAS will droop less than –1V, causing an A/D overflow.VMEAS with valid connections:For valid connections, INPUT Sense HI, VMEAS, will dip during the 4 ms IOPENLEAD phase. The amountof the voltage dip is the sum of IOPENLEAD and the range ISOUR and RDUT load. For example, ifmeasuring a 100 kΩon the 100 kΩrange, the VMEAS across the 100 kΩ will be 0.85 V (10 A to1.5 μA) × 100 KΩduring IOPENLEAD and 1 V during measurement phase.The tables below note timing with dmm.opendetector = dmm.ON.Range SHI and SLOIOPENLEADphase (ms)1SHI settlingtime (ms)Line frequency(Hz)SHI measurement time(ms)1-10 kΩ 4.0 0.5 60 min max0.0083 25050 0.010 240100 kΩ 4.0 2.0 60 0.0083 25050 0.010 2401 MΩ 4.0 30.0 60 0.0083 25050 0.010 24010 MΩ to100 MΩ4.0 5.01 60 0.0083 250Range InternalDMM comm(ms)SLOsettlingtime (ms)SLOmeasurementtime (ms)InternalDMM comm1 kΩ to10 kΩ0.06 0.5 min max 0.060.0083 2500.010 240100 kΩ 0.06 1.0 0.0083 250 0.060.010 2401 MΩ 0.06 1.0 0.0083 250 0.060.010 240
