Fluke 8808A User Manual - Page 94

8808A Users Manual Primary Display REL HOLD Table A-2. Sample Dual Display Applications (cont.) Secondary Display Resistance Actual Value Applications • Select and sort resistors. (See also "Using the Compare Function" in Chapter 3.) • Show actual measurement while holding a previous, stable measurement on the primary display 2W/4W HI INPUT V SENSE 4W HI 1000V 750V MAX LO 200 mA MAX 1000 V 600 V CAT I CAT II 300 V 1V LO 500 Vpk 10 A MAX mA 10 A 8808A 5-1/2 DIGIT MULTIMETER Figure A-2. DC Voltage and DC Current Measurement on Input Signal eue27.eps The lead from the internal measuring circuitry of the meter to the LO terminal (on the front panel) is the same for both voltage and current measurements. The resistance of this lead is approximately .003 ohm. If current is being measured, therefore, a voltage drop will occur in the resistance that is common to both circuits. This internal resistance, when added to the external resistance of the lead from the COM input terminal will affect the accuracy of the voltage reading. For instance, if the external lead resistance is .007 ohm, the "total" common resistance is .010 ohm. If there is 1 A of current, the voltage reading would be affected by (1 A x.01ohm ) = .01 V or 10 m V. Depending on the circumstances, this may be significant. If you want to measure dc voltage on an input signal in the primary display and dc current in the secondary display, proceed as follows: 1. Turn the Meter on 2. Press D to select the dc voltage function for the primary display. 3. Press Q then E to select the dc current function for the secondary display. 4. Connect the leads to the test circuit as shown in Figure A-2 and read the measurements on the display. Although current will be displayed as negative, it is in fact positive when interpreted according to current flow convention. A-4