231 Active Filter

Refer to Figure 2-7. The two-pole active filter consisting of A1R21, A1R22, A1C12, and A1C13 filters noise on the a-d converter input signal for the DCV, DCmA, DCA, OHMS, kOHMS, and Diode Test functions. Resistor A1R22 provides a 200-kW input impedance for the filter, except as follows:

• Resistors A1R6 and A1R7 provide the 200-kW input impedance for the 100 mV dc, 300 mV dc, 1000 mV dc, 3 V dc, ohms, and kilohms ranges.

• Resistor A1R10 and the 100.5 kW resistor in A1Z1 provide the 200 kW impedance for the 10 V and 30 V dc ranges.

• Resistor A1R4 provides the impedance for the two DCmA ranges.

Analog Measurement Processor switch S82 shorts out A1R21 during ranging. Switch S87 shorts out A1R22 both during ranging and in the measurements listed above. For the 1000 kW, 3 MW, 10 MW, 30 MW, 100 MW, and 300 MW ranges, the active filter is bypassed, and switch S83 selects C14 as the filter.

ACTIVE FILTER INPUT

A1C12

A1C13

M W FILTER

A1R22

A1C12

A1C13

qb07f.eps

Figure 2-7. Active Filter Simplified Schematic

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