5 Theory of Operation
138 Keysight 34970A/34972A Service Guide
Input
Unless otherwise noted, components in this discussion are located on the A4
circuit assembly (34970-66504).
The purpose of the Input section is to connect the Input HI terminal to the various
measuring functions. This is accomplished through K102, K103, and K104.
Additionally, connections are made for the 4-wire ohms
HI Sense and LO Sense inputs. Shunt selection (ranging) and voltage sensing are
also performed for the current function. The table below shows the state of each
relay for each measuring function. All relay coils are driven from U150.
Functional K102 K103 K104 Sense at:
0.1 V - 10 VDC
100 V - 300 VDC
2-Wire Ohms
4-Wire Ohms
AC Voltage
Frequency/Period
3 A, 1A DCI
100 mA, 10 mA DCI
1A AC I
Set
Set
Reset
Reset
Set
Set
Reset
Set
Reset
Set
Reset
Set
Set
Reset
Reset
Reset
Reset
Reset
Set
[a]
Set
Reset
[b]
Reset
[b]
Reset
Reset
Reset
Reset
Set
[a] K104 will be reset when input resistance is selected to >10,000 MW through the menu.
[b] K104 will be set for the 100 MW range.
U101-5
U102-12
U101-5
[c]
AC_IN
AC_IN
U101-10
U101-10
AC_IN
[c] Configurations shown are for the current source output (HI) terminal. The measurement sense is accomplished
through the Sense HI / Sense LO terminals.
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