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參數(shù)資料
| 型號： | EVAL-AD7751EB |
| 廠商： | Analog Devices, Inc. |
| 英文描述： | Energy Metering IC With On-Chip Fault Detection |
| 中文描述： | 電能計量IC，帶有片上故障檢測 |
| 文件頁數(shù)： | 16/16頁 |
| 文件大?。?/td> | 249K |
| 代理商： | EVAL-AD7751EB |
REV. A
–16–
C
P
AD7751
The F
1–4
frequencies allow complete coverage of this range of
output frequencies on F1 and F2. When designing an energy
meter, the nominal design voltage on Channel 2 (voltage) should
be set to half-scale to allow for calibration of the meter constant.
The current channel should also be no more than half-scale when
the meter sees maximum load. This will allow over-current signals
and signals with high crest factors to be accommodated. Table
VI shows the output frequency on F1 and F2 when both analog
inputs are half-scale. The frequencies listed in Table VI align
very well with those listed in Table V for maximum load.
Table VI.
Frequency on F1 and F2 –
CH1 and CH2
Half-Scale AC Inputs
S1
S0
F
1–4
1.7
3.4
6.8
13.6
0
0
1
1
0
1
0
1
0.085 Hz
0.17 Hz
0.34 Hz
0.68 Hz
When selecting a suitable F
1–4
frequency for a meter design, the
frequency output at I
MAX
(maximum load) with a meter constant
of 100 imp/kWhr should be compared with Column 4 of Table
VI. The frequency that is closest in Table VI will determine the
best choice of frequency (F
1–4
). For example if a meter with a
maximum current of 25 A is being designed, the output frequency
on F1 and F2, with a meter constant of 100 imp/kWhr, is 0.153 Hz
at 25 A and 220 V (from Table V). Looking at Table VI, the
closest frequency to 0.153 Hz in column four is 0.17 Hz. There-
fore F
2
(3.4 Hz—see Table II) is selected for this design.
Frequency Outputs
Figure 1 shows a timing diagram for the various frequency
outputs. The outputs F1 and F2 are the low frequency outputs
that can be used to directly drive a stepper motor or electrome-
chanical impulse counter. The F1 and F2 outputs provide two
alternating low going pulses. The pulsewidth (t
1
) is set at 275
ms and the time between the falling edges of F1 and F2 (t
3
) is
approximately half the period of F1 (t
2
). If, however, the period
of F1 and F2 falls below 550 ms (1.81 Hz), the pulsewidth of
F1 and F2 is set to half of their period. The maximum output
frequencies for F1 and F2 are shown in Table III.
The high-frequency CF output is intended to be used for
communications and calibration purposes. CF produces a
90-ms-wide active high pulse (t
4
) at a frequency that is propor-
tional to active power. The CF output frequencies are given in
Table IV. As in the case of F1 and F2, if the period of CF (t
5
)
falls below 180 ms, the CF pulsewidth is set to half the period.
For example, if the CF frequency is 20 Hz, the CF pulsewidth
is 25 ms.
NO LOAD THRESHOLD
The AD7751 also includes a “no load threshold” and “start-up
current” feature that will eliminate any creep effects in the
meter. The AD7751 is designed to issue a minimum output
frequency. Any load generating a frequency lower than this
minimum frequency will not cause a pulse to be issued on F1,
F2, or CF. The minimum output frequency is given as 0.0014%
of the full-scale output frequency for each of the F
1–4
frequency
selections (see Table II). For example, an energy meter with a
meter constant of 100 imp/kWhr on F1, F2 using F
2
(3.4 Hz),
the maximum output frequency at F1 or F2 would be 0.0014%
of 3.4 Hz or 4.76
×
10
–5
Hz. This would be 3.05
×
10
–3
Hz at
CF (64
×
F1 Hz). In this example the no load threshold would be
equivalent to 1.7 W of load or a start-up current of 8 mA at 220 V.
Comparing this value to the IEC1036 specification, which states
that the meter must start up with a load equal to or less than
0.4% Ib. For a 5 A(Ib) meter 0.4% of Ib is equivalent to 20 mA.
24-Shrink Small Outline Package
(RS-24)
24
1
13
12
0.328 (8.33)
0.318 (8.08)
0.311 (7.9)
0.301 (7.64)
0.212 (5.38)
0.205 (5.207)
PIN 1
SEATING
PLANE
0.07 (1.78)
0.066 (1.67)
0.008 (0.203)
0.002 (0.050)
(0.65)
BSC
0.078 (1.98)
0.068 (1.73)
0.015 (0.38)
0.010 (0.25)
0.009 (0.229)
0.005 (0.127)
0.037 (0.94)
0.022 (0.559)
8
°
0
°
24-Lead Plastic DIP
(N-24)
24
1
12
13
PIN 1
1.275 (32.30)
1.125 (28.60)
0.280 (7.11)
0.240 (6.10)
0.195 (4.95)
0.115 (2.93)
0.015 (0.381)
0.008 (0.204)
0.325 (8.25)
0.300 (7.62)
SEATING
PLANE
0.060 (1.52)
0.015 (0.38)
0.210
(5.33)
MAX
0.022 (0.558)
0.014 (0.356)
0.200 (5.05)
0.125 (3.18)
0.150
(3.81)
MIN
0.100
(2.54)
BSC
0.070 (1.77)
0.045 (1.15)
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
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