Operation - AEMC 1000N Calibration Manual

MODEL 1000N

OPERATION:

a) Mode of Operation for MΩ and GΩ:
An oscillator (Z1) provides a low voltage signal which is amplified by the transformer (T1) then
rectified and filtered (CR201, C201). This high DC voltage is regulated through the divider (R202
to R209) and the operational amplifier (Z4).
When the range switch is turned to select a new voltage range, the input of (Z4) is open. In
order to prevent an increase in the high voltage, two diodes (CR12 and CR13) are connected to
the + supply in order to always bring the output of Z4 to the + supply and stop the oscillation of
Z5 and the high voltage.
Because RM is significantly lower than RX, the portion of the curve which is used, VM =f (RX ) ,
can be expressed as a function
Measurement for the M Ω range with test voltages of 50 and 100 Volts is performed by
measuring the voltage drop on the shunts R101 and R102. For test voltages of 250, 500, 1000
Volts is performed through the current shunt R102 only.
Measurement for the G Ω range is performed by measuring the voltage drop on the shunt R103.
The resulting voltage is then filtered and passed through a variable gain amplifier (Z5) then into
a logarithmic amplifier (Z4). Temperature compensation is provided to the amplifier by a
thermistor (TH1). The last amplifier (Z7) provides the current needed to drive the meter
movement G1.
A negative 4.6 Volt supply is provided by (Z3) for powering the quad amplifier (Z2).
4/21/2005
REPAIR AND CALIBRATION MANUAL
VHT
CR
HV GENERATOR
DIVIDER BRIDGE
(
VHT
RX =
VM
K
.
RX
REV. 7: March 13, 2004
FILE LOCATION: Manuals - Cal. Man - 1000MAN.DOC
-
+
RX
LOGARITHMIC
Vm
RM
Vd
MEASURING SHUNT
)
VHT ∗ RM
= ~
1
RM, or VM
K
VM =
RX
7
CAT. #185.100
AMPLIFIER
G
RX