HP 3478A Technical Manual page 96

3478A 3478A
c. c. Oh Ohm m s F s Fun unct ctio ion. n.
selected, the Ohms Current Source supplies a known dc selected, the Ohms Current Source supplies a known dc
current to to the current the unknown unknown resistance.
proportional to the unknown resistance and the current is proportional to the unknown resistance and the current is
applied to to the applied the Input Input Terminals.
measurement is then made (see step b) and the ohms measurement is then made (see step b) and the ohms
reading is calculated by the Main Controller circuitry reading is calculated by the Main Controller circuitry
using the zero measure- ment (see step f) and using the zero measure- ment (see step f) and
calibration constant(s). calibration constant(s).
d. d. A A C Vo C Volt lts Fu s Func ncti tion
selected, the input is connected to the AC to DC Con- selected, the input is connected to the AC to DC Con-
verter. verter. The converter The converter changes
equivalent (RMS) dc voltage and applies it to the A/D equivalent (RMS) dc voltage and applies it to the A/D
Converter. The A/D Converter. The A/D Converter ch Converter changes the
digital information and applies it to the A/D Con- troller. digital information and applies it to the A/D Con- troller.
The A/D Controller passes it on to the main controller The A/D Controller passes it on to the main controller
which calculates the correct reading using the which calculates the correct reading using the
Figure 7-F-1. 3478A Simplified Figure 7-F-1.
If the Ohms Function is If the Ohms Function is
resistance. A volt A voltage d age drop
Terminals. A A regular regular dc
on. . If the AC Volts Function is If the AC Volts Function is
changes the the voltage voltage to to its its
anges the voltage to voltage to
3478A Simplified Block Diagram Block Diagram
zero zero measurement measurement
constant(s). constant(s).
rop
e. e. AC AC Cur
dc Current or DC Current Functions are selected, the input Current or DC Current Functions are selected, the input
current is applied to re current is applied to resistor R107 (.
ant voltage drop across the resistor is then measured. ant voltage drop across the resistor is then measured.
An ac or dc volts measurement is made, dependent on An ac or dc volts measurement is made, dependent on
the function selected (AC Current or DC Current, the function selected (AC Current or DC Current,
respectively). respectively).
f. f. A A ut utoz
Function is enabled, an offset measurement (known as a Function is enabled, an offset measurement (known as a
zero zero measurement) measurement)
measurement. measurement.
connecting the input of the Input Amplifier (HI INPUT connecting the input of the Input Amplifier (HI INPUT
Terminal is open) t Terminal is
resultant offset of resultant offset of
7-F-2 7-F-2
(see (see step step
Curren rent or t or DC C DC Curr urrent ent Fun
sistor R107 (.1 ohm).
ozer ero o Fu Func ncti tion on. . If the 3478A's Autozero If the 3478A's Autozero
is is made made
The The zero zero measurement measurement is is made
open) to ground o ground (LO INPUT Terminal). (LO INPUT Terminal). The
TM 11-6625-3071-14 TM 11-6625-3071-14
f) f) and and calibration calibration
Functi ction. on. If the AC If the AC
1 ohm). The result- The result-
before before an an input input
made by by
The