87 V/AN
Service Manual
12
The Meter uses diode clamps, a positive temperature coefficient thermistor, metal oxide
varistors (MOVs) and fuses for protection when inadvertent overload conditions are
applied across the input terminals. Table 12 shows the components that limit and direct
overload currents to prevent damage to the Meter.
Table 12. Overload Protection Components
Function Components Protected Protection Components
U1 pin 3 Z1(9.997 M), U1-3 clamps K
VAC
S1(1,2)(1,3)(29,5)(4,5), Z1(9.997 M) RT1, R1, RV1, RV2, Z2, RV3
U1 pin 3 Z1(9.997 M), U1-3 clamps V
VDC
S1(1,2)(29,5)(4,5), Z1(9.997 M) RT1, R1, RV1, RV2, Z2, RV3
U1 pin 36 RT1, R1, CR10, VR1, CR8, CR9, R3, U1-36
clamps
U1 pin 3 RT1, R1, CR10, VR1, CR8, CR9, Z1(9.997 M),
U1-3 clamps
U1 pin 1 RT1, R1, CR10, VR1, CR8, CR9, R85, U1-1
clamps
m
L, d
mV dc, Temperature
S1(4,5) Z2, RV3, RV2, RT1, R1, CR10, VR1, CR8,
CR9
U1 pin 36 RT1, R1, CR10, VR1, CR8, CR9, R3, U1-36
clamps
U1 pin 3 RT1, R1, CR10, VR1, CR8, CR9, Z1(9.997 M),
U1-3 clamps
U1 pin 1 Z2, R85, U1-1 clamps
T, E,X
Ohms, Capacitance,
Continuity
S1(29,5) RT1, R1, CR10, VR1, CR8, CR9
U1 pin 36 RT1, R1, CR10, VR1, CR8, CR9, R3, U1-36
clamps
U1 pin 3 RT1, R1, CR10, VR1, CR8, CR9, R2, C1,
Z1(9.997 M), U1-3 clamps
U1 pin 1 Z2, R85, U1-1 clamps
G
Diode Test
S1(1,3)(29,5) RT1, R1, CR10, VR1, CR8, CR9
S1(7,8)(7,6) F1, CR1, CR2 Voltage applied to
mA/µA input jack in
any of the above
functions or OFF
U2 pin 3 after F1 opens R7, CR5
R5 F1, CR1, CR2, R6 mA/A
U2 pin 3 after F1 opens R7, CR5
R4 F1, CR1, CR2 µA
U2 pin 3 after F1 opens R7, CR5
R6 F2 (assuming enough current is available) Voltage applied to A
input jack in any
function including OFF
U2 pin 2 after F2 opens R10, CR6
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