Fluke 189II/AN, Руководство по обслуживанию

Страница: 19 / 48

True-rms Digital Multimeter
Theory of Operation
11
Theory of Operation
The Meter includes the following major modules: Case, Display Module, Batteries,
Shields, and the Printed Circuit Assembly (PCA).
All the electrical processing is done on the PCA.
There are four main sections of the PCA: analog signal conditioning and conversion,
measurement processor, memory, and power supply.
Analog Signal Conditioning
The Analog Signal Conditioning section converts all levels of voltage and currents, AC
and DC, at the input terminals to a DC voltage that is read by the Analog to Digital
Converter (ADC). It also provides the stimulus current and voltages for the Ohms,
Continuity, Diode Test and Capacitance functions. This section provides protection
against overloads on the input terminals.
The Analog Signal Conditioning section is controlled by the measurement processor. It
gets the range and function from the master control section. It, in turn, sets up all the
analog switches, starts the ADC, reads the ADC, and sends this back to the control
processor. It has timers to count for the frequency functions. It monitors and reports back
to the control processor the position of the rotary switch, the level of the battery, and the
use of the current jacks.
Control Section
The Control Section contains a
μ
P and memory. It receives information on the position of
the rotary selector switch, key presses, and measurement
μ
P data. It outputs range and
function selection to the measurement
μ
P and data to the display module. It also reads
from and writes to memory.
Power Supply
This section takes the battery voltage from the six AA cells, which can be from 6 to
9 volts, and creates 1.8 V, 2.5 V, 3 V, 5 V and 20 V which are switched on and off. It
also creates a 3 V supply that is always on.