| |
|
|
|||||
| |
|||||||
| |
|
|
|
|
|
||
| |
|
|
|
|
|
|
|
4010/4011 Digitize Meter Improvements description
Prodigit electronic continuous effort for improvement beyond perfection and "Customer satisfaction, best quality" policy; other than continuously develop all kind of test equipment, Prodigit also put an enormous effort improving existing product. This article is describing 4010/4011 changes in detail and its advantage, 4010/4011 has two major changes, its description are as follow, about power meter's theory and its design, please refer to Prodigit 1996/1997 product's application description on Application Note- 400 "Basic of Power Meter."
1. Voltage measuring part:
This portion is
from original single input circuit (figure1) change into differential input
circuit (figure 2).
Figure 1: single input circuit block diagram
Figure 2: differential input circuit block diagram
1.1. Advantage for the change:
1.1.1. It can be more accurately when measuring voltage across load: After
changing the single input circuit into differential input voltage measuring
circuit, we can measure the voltage on the load without voltage drop across
the cable which decreases the accuracy. It becomes apparent especially when
there are large load current or long cable connection. The difference is describe
in figure 3, original single input circuit can only measure the voltage across
the 4010/4011 rear panel's load input connector (voltage V1 or terminal a-b
in figure 3), if measuring load has large current or long cable connection,
its voltage drop across the cable can not be compensate, which will cause inaccuracy.
As for differential circuit, it can solve this problem, together with suitable
cable connection, it can measure load side's input circuit (Load voltage V2
or Load terminal a'-b' in Figure 3), therefore above large current or long cable
connection error can be eliminated.
Figure 3 differential input can eliminate test circuit's voltage drop in
cable
1.1.2. Easier Calibration:
During calibration 4010/4011 power meter, it needs voltage and current input
in order to calibrate correctly, also because 4010/4011 use real time A/D voltage
and current waveform sampling technique, (similar to digital oscilloscope CH
1, CH 2, sampling simultaneously), therefore voltage and current need to be
in same phase in order to meet the normal test connection and loading condition.
(Actually meter calibrator is used to simulate actual condition) because of
that voltage and current in phase is necessary, therefore for single input 4010/4011,
calibrator's voltage and current output need to have insulation capability in
order to have correct phase for voltage and current output, describe as follow:
Figure 4: 4010/4011 single input circuit calibration connecting circuit
If there is no specific instruction, usual calibrator negative connector
circuit connect to ground. Even though it doesn't affect the traditional power
meter which using PT/CT isolation technique (shown in figure 5), but not for
4010/4011, the problem is that they cannot match, as describe in figure 5:
Figure 5: Traditional power meter's calibration connecting circuit
After 4010/4011 change from single input circuit to differential input circuit,
its voltage input and current measuring is not connected together inside the
power meter anymore, therefore during calibration it doesn't matter if the calibrator's
voltage and current input is insulate or using the same ground, as describe
in figure 6:
Figure 6: The calibration circuit connection of differential input 4010/4011
power meter
1.2. Accessories
changes:
4010/4011 accompany
accessories test adapter provide 4010/4011 simple plug into house hold electricity
and simple load connection, and because the changes in input circuit to differential
input circuit, accessory also change accordingly. In the mean time, internal
connection is done according to the operator known connection method, plus providing
system connection on the case for reference, the rear panel of 4010/4011 connector
are shown as follow:
Figure 7: 4010/4011 single input circuit rear panel connection
Figure 8: 4010/4011 differential input circuit rear panel connection
Test adapter connection figure description:
Figure 9: 4010/4011 single input circuit's schematic diagram for internal connection
Figure 10: 4010/4011 differential input circuit's schematic diagram for internal
connection
2. Frequency lock loop change from Analog Feedback Circuit to Digital
Feedback Circuit:
2.1.
Theory Description:
4010/4011 use Analog Feedback Circuit to get voltage/current waveform sampling
frequency to 256 times of line frequency. Its voltage, current A/D resolution
is 12 bit for each sampling. In another word, if input voltage frequency is
50 Hz, its voltage/current sampling frequency is 12.8 KHz, if 60 Hz, then it
will be 15.36 KHz. If sampling frequency can synchronize with input voltage
frequency, its block diagram will be like figure 11:
Figure 11: Analog Feedback Circuit block diagram
( Large picture
)
Digital Feeback Circuit function has the same function as Analog Feedback Circuit; its block diagram is shown in figure 12:
2.4.3. For no input signal or DC measurement (like no connection or floating), operator can manually set sampling frequency or allow it to automatically switch, set the sampling frequency to 50 Hz, 60 Hz, or synchronize with line frequency. Therefore the sampling frequency can synchronize with line frequency, eliminate line (50/60 Hz) frequency disturbance, therefore, it can get more stable and accurate results.
2.4.4. For input signal with only two or more zero crossing (for example UPS output frequency), can cause input frequency rectifier circuitry produce frequency two times the actual frequency, causing sampling frequency error (mistaken for 100 Hz or 120 Hz), under this circumstance, operator can set sampling frequency to 50Hz, 60Hz or synchronize with household line frequency, therefore it is suitable for any situation, for detail operation setting, please refer to 4010/4011 operator manual.
