Chapter 1 Functional Overview And Digital Display; System Configuration And Block Diagram - YOKOGAWA WT200 User Manual

Chapter 1 Functional Overview and Digital Display

1.1

System Configuration and Block Diagram

System Configuration
Block Diagram
VOLTAGE INPUT
CURRENT INPUT
IM 253421-01E
PT
Voltage
Equipment
under
Current
test
CT
Ext.
sensor
INPUT
A/D
ISO
Zero Cross
Detector
LPF
A/D
ISO
Zero Cross
Detector
LPF
EEPROM
This instrument consists of various sections: input (voltage input and current input
circuits), DSP, CPU, display and interface section.
In the voltage input circuit, the input voltage is formalized by a voltage divider and
operational amplifier, then sent to the A/D converter.
In the current input circuit, the input current passes through a shunt resistor that forms
a closed circuit. The voltage across shunt resistor is amplified and normalized and
then input to the A/D converter. This method enables switching of the current range
without opening the current measurement circuit, so the current range can be switched
while electricitiy is supplied to the circuit. This also enables remote control via
communications outputs.
The output from the A/D converter in the current input and voltage input circuits is sent
to the DSP (Digital Signal Processor) via a photo-isolator, which is used to provide
insulation between the current input circuit (or voltage circuit) and the DSP. One DSP
is provided for each input element (current/voltage). For example, a total of 3 DSP's
are used for the three-phase, four-wire model. The DSP performs averaging of
voltage, current and active power for each sampled data sent from the A/D converter.
After processing of a certain number of sets of data has been completed, computation
of apparent power, reactive power, power factor and phase angle starts.
Computation results are then sent from the DSP to the CPU, where computation such
as range conversion, and scaling is carried out. Control of display and outputs is also
performed by the CPU.
Input
either
input
one
WT200
(253421)
Input
input
either
one
A/D Bus
DSP
interface
Arbiter
Lead/Lag
Detector
FREQUENCY
COUNTER × 2
CLOCK
HARMONICS
PLL
DMAC
RAM
(Option)
Contact / relay output
Analog output
Recorder
GP-IB or
Personal
RS-232-C
Computer
Ext. printer
or plotter
CPU
CPU
SAMPLING
CLOCK
ROM
RAM
KEY&DISPLAY
CONTROLLER
GP-IB
or
RS-232-C
D/A OUTPUT
EEPROM
(Option)
COMPARATOR
Bus
Arbiter (Option)
1
1-1