Fluke Portable Multimedia Player 8842a Manual De Usuario
Theory of Operation
PRECISION VOLTAGE REFERENCE
5
5-11
5-11. Settling Configuration
The circuit assumes a settling configuration between the track and hold configurations.
The circuit assumes the configuration in Figure 5-4B for unity gain and the configuration
in Figure 5-4C for gain of 10.
The circuit assumes the configuration in Figure 5-4B for unity gain and the configuration
in Figure 5-4C for gain of 10.
During this time the DC Scaling circuit is still connected to the T/H amp. However,
changes in the input do not affect the value to be measured, which is stored on C308.
changes in the input do not affect the value to be measured, which is stored on C308.
5-12. Hold Configuration
The X1 hold configuration (Figure 5-4D) is used for all VDC ranges except r1 and for all
ohms ranges except r1. The output of U307 is the negative of the input voltage.
ohms ranges except r1. The output of U307 is the negative of the input voltage.
The X10 hold configuration (Figure 5-4E) is used for the mA DC function, the 200 mV
dc range, and the 200
dc range, and the 200
Ω
range, and provides a gain of 10.
5-13. Pre-Charge Configuration
The pre-charge configuration (Figure 5-4F) occurs after the hold configuration in VDC
ranges r1, r2, and r4, and ohms ranges r1, r2, r3, and r4. U306 is connected as a buffer to
charge stray capacitance at the non-inverting input of the T/H Amplifier. The pre-charge
configuration is not used in any other ranges.
ranges r1, r2, and r4, and ohms ranges r1, r2, r3, and r4. U306 is connected as a buffer to
charge stray capacitance at the non-inverting input of the T/H Amplifier. The pre-charge
configuration is not used in any other ranges.
5-14. PRECISION VOLTAGE REFERENCE
The Precision Voltage Reference (Figure 5-6) provides precise reference voltages of -
7.00000 and +7.00000. The reference element is a reference amplifier (ref amp). The
nominal ref amp voltage is 6.5V.
7.00000 and +7.00000. The reference element is a reference amplifier (ref amp). The
nominal ref amp voltage is 6.5V.
f5-06.wmf
Figure 5-6. Precision Voltage Reference