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ADE7757EB Datasheet(PDF) 2 Page - Analog Devices |
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ADE7757EB Datasheet(HTML) 2 Page - Analog Devices |
2 / 11 page PRELIMINARY TECHNICAL DATA REV. PrF EVAL-ADE7757EB –2– ANALOG INPUTS (SK1 AND SK2) Voltage and current signals are connected at the screw termi- nals SK1 and SK2 respectively. All analog input signals are filtered using the on-board antialias filters before being pre- sented to the analog inputs of the ADE7757. Some analog inputs offer additional signal conditioning, e.g., attenuation on the voltage channel. The default component values included with the evaluation board are the recommended values to be used with ADE7757. The user can easily change these compo- nents, but this is not recommended unless the user is familiar with sigma-delta converters as well as the criteria used for se- lecting the analog input filters—see ADE7757 datasheet. Voltage Input SK2 is a two-way connection block that can be directly connected to a high voltage source, e.g., 220 V rms. The resistor network R15 (trim pot), R19, R20, R21, and R22 make up a very flexible attenuation and calibration net- work—see schematic. The attenuation network is designed such that the corner frequency (–3 dB frequency) of the network matches that of the RC (antialiasing) filters on the other analog inputs. This is important, because if they do not match there will be large errors at low power fac- tors. Figure 1 shows how the attenuation network may be used with fixed resistors or the trim pot. The trim pot allows the voltage signal on V2P to be scaled to calibrate the frequency on CF to some given constant, e.g., 100 imp/kWhr. Some examples are given later. JP5 JP6 R19 C18 R15 R20 R22 JP18 A B JP17 SK2A V2P R21 a. Attenuation Using Trim Pot (R15) JP5 JP6 R19 C18 R15 R20 R22 JP18 A B JP17 SK2A V2P R21 b. Attenuation Using Fixed Resistors Figure 1. Attenuation Network on Channel 2 If Channel 2 is being used in a single-ended mode of op- eration, the unused input of the pair should be connected to analog ground (AGND) via an antialias filter. This is shown in Figure 2 where V2N is connected to AGND using jumper JP8. JP8 R18 C19 TP5 V2N JP7 SK2B Figure 2. Unused Analog Inputs Connected to AGND All passive components (resistors and capacitors) which make up the attenuation network and antialias filters may be modified by the user. The components are mounted using PCB jack sockets for easy removal and replacement of components. Current Input SK1 is a two-way connection block, which allows the ADE7757 to be connected to a current sensor through one differential input channel. In this example, we chose a shunt as the current sensor. Figure 3 shows a typical connection dia- gram for shunt connection. SHUNT AGND SK1A SK1B ADE7757 JP1 JP2 R16 C16 TP1 V1P JP3 R17 C17 TP2 JP4 V1N SK1C Figure 3. Typical Shunt Connection for Channel 1 EVALUATION BOARD SETUP (ANALOG INPUTS) Figure 4 shows how the ADE7757 evaluation board can be set up for a simple evaluation. Two signal generators are used to provide the sinusoidal (ac) signals for Channel 1 and Channel 2. The user must have some way of phase locking the genera- tors. Also if the ADE7757 performance-over-power factor is being evaluated, two separate signal sources will be required. The generators are shown connected in a single-ended configu- ration. The grounded analog inputs of Channel 1 and Channel 2 (V1N and V2N) are connected to AGND via an antialias filter. In Figure 4, analog input V2N is grounded via R21 and R22. The capacitor C18 is connected in parallel. |
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