Cirrus Logic Power-Meter ICs Guide
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To introduce Cirrus’s power measurement ICs, and its operations
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Cirrus Logic Power-Meter ICs Guide
- 4. Cirrus’ Product Portfolio Parts Channels Energy Pulse Outputs Instantaneous I & V Real Active Power I RMS , V RMS Apparent Power Reactive Power Temp Sensor CS5460A 2 CS5461A 2 CS5462A 2 CS5463A 2 CS5464A 3 CS5466A 2 CS5467A 4
- 5. Signal Path Current Input Voltage Input Pulse Output
- 10. Single Phase 2-Wire Application Circuit Current sensing Voltage sensing
- 11. Single Phase 3-Wire Application Circuit Current Transformer Voltage Dividers
Notas do Editor
- Welcome to the training module on CS546x Power-Meter ICs.
- This training module introduces Cirrus’s power measurement ICs, and it’s operations.
- The industry requirements for electricity metering are evolving rapidly and becoming more challenging for both the meter design companies and the providers of electricity metering equipment. The electric utility and the energy consumer want accurate metering, and often across a very wide dynamic range. Compared to traditional mechanical electricity metering devices, the power measurement ICs may specify a measurement range of 1000:1. That is, the power flow must be measured accurately with the current input changing over a 1000 to 1 range. The maximum error specification for the power measurement device is typically 0.1% of the parameter being measured over the specified dynamic range.
- To meet the differing needs of power measurement, Cirrus developed different ICs with a high degree of commonality and some interesting differences. These ICs combine 2 or 4 delta-sigma analog-to-digital converters channels followed by a computation engine that performs power calculations and energy to pulse conversion. These ICs are able to accurately measure instantaneous current and voltage while calculating instantaneous power, real power, apparent power, I RMS , and V RMS . For the electrical meter market where reliability and accuracy are key, Cirrus Logic’s solution provides the design flexibility to help makers of residential power meters reduce costs and get to market faster with a better-quality power meter product.
- The figure shows two data paths. The analog inputs are structured with two dedicated channels, voltage and current, then optimized to simplify interfacing to sensing elements. The voltage-sensing element introduces a voltage waveform on the voltage channel input and is subject to a fixed 10x gain amplifier. Simultaneously, the current sensing element introduces a voltage waveform on the current channel input and is subject to a programmable gain amplifier. Both amplified signals are sampled by delta-sigma ADCs for digitization. The single-bit data is passed to the low-pass decimation filter and output at a fixed word rate. A digital high-pass filter removes any DC component from the selected signal path. After filtering, the instantaneous voltage and current digital codes are subjected to offset/gain adjustments. The digital instantaneous voltage and current data is then processed further. The calibrated energy value is then converted into a pulse output stream with a average frequency proportional to the measured energy.
- These devices perform measurements of instantaneous current and voltage. And from this, perform computations of the corresponding instantaneous power, as well as periodic calculations of real energy, RMS current, and RMS voltage. The measurement or calculation results are available in the form of 24-bit signed and unsigned words. All measurements are available as a percentage of full scale.
- The power measurement ICs provide three output pins for energy registration. Each pin’s pulse output represents a predetermined quantity of energy based on the different parts and configuration. The quantity of energy represented in one pulse can be varied by adjusting the value in the Pulse-Rate Register. Let’s look at the pulse output of CS5467. By default, E1 outputs total active energy, E3, total reactive energy, and E2, the sign of both active and reactive energy.
- Except CS5462 and CS546, other CS546x power measurement ICs provide a serial interface for communication between a host microcontroller. If the devices have 5 pin serial interface, they can be connected a serial EEPROM instead of a host microcontroller. The serial port incorporates a serial port transmit and receive buffer with a command decoder that interprets one-byte (8 bits) commands as they are received. The serial port can be configured synchronous or unsynchronized communication.
- Except CS5462 and CS546, other CS546x power measurement ICs offer digital DC offset and gain compensation that can be applied to the instantaneous voltage and current measurements, and AC offset compensation to the voltage and current RMS calculations. Since the voltage and current channels have independent offset and gain registers, offset and gain calibration can be performed on any channel independently. During offset calibrations, no line voltage or current should be applied to the meter. A zero-volt differential signal can also be applied to the voltage inputs or current inputs. During gain calibration, a full-scale reference signal must be applied to the meter or optionally, scaled to the voltage and current inputs. A DC reference must be used for DC gain calibration. Either an AC or DC reference can be used for RMS AC calibrations. If DC is used, the associated high-pass filter (HPF) must be off.
- This figure shows the CS5464 configured to measure power in a single-phase, 2-wire system while operating in a single-supply configuration. In this diagram, a shunt resistor is used to sense the line current and a voltage divider is used to sense the line voltage. In this type of shunt-resistor configuration, the common-mode level of the CS5464 must be referenced to the line side of the power line. This means that the common-mode potential of the CS5464 will track the high-voltage levels, as well as low-voltage levels, with respect to earth ground. Isolation circuitry is required when an earth-ground-referenced communication interface is connected. A current transformer (CT) is connected to the return line current, which implements the tamper detection circuit.
- This diagram shows a single-phase, 3-wire system. In many 3-wire residential power systems within the United States, only the two line terminals are available. Similarly, it uses voltage dividers to sense the line voltage. But it uses a current transformer to sense the line current. This transformer provides complete isolation from the power lines.
- Thank you for taking the time to view this presentation on “ CS546x Power-Meter ICs” . If you would like to learn more or go on to purchase some of these devices, you may either click on the part list link, or simply call our sales hotline. For more technical information you may either visit the Cirrus Logic site, or if you would prefer to speak to someone live, please call our hotline number, or even use our ‘live chat’ online facility. You may visit Element 14 e-community to post your questions.