Position encoding in battery-powered electronics: Page 4 of 5

October 09, 2014 //By Jonas Kupp and David Lin
Position encoding in battery-powered electronics
Jonas Kupp and David Lin consider the benefits of position encoding in battery-powered electronics.
restart occurs with false data. Therefore, all continued movement in these actuators has to be safely detected by a multiturn encoder. They either have a mechanical gear or an electronic recording with power failure protection, e.g. through a battery. For consumption measurement devices, such as industrial gas or water meters, the acquisition has to be possible even without external supply voltage. An automatic switching between battery and external supply is then necessary.

Figure 3 shows the block diagram of a gas or water meter using the iC-PV to magnetically scan an impeller. This ULP 1-chip Hall encoder automatically switches between energy-saving battery operation and normal grid operation.

If the supply voltage VDD falls below a defined level, the iC-PV automatically switches to battery supply VBAT. After the power supply has been restored, the iC-PV provides the readout device with the counter value via a serial interface for the consumption calculation. The measuring results are checked via 8-bit CRC and errors are indicated via an active-low NERR output as well as an error bit within the serial data transmission.

Four Hall sensors detect position changes with an adjustable 1- to 3-bit resolution. The number of rotations is counted in a multiturn counter with a length of up to 40 bits. The iC-PV also has parallel outputs for octal resolution of 3 bits. The external EEPROM is programmed during calibration via a separate I²C interface and the iC-PV loads the CRC-secured configuration data at power-up.

The iC-PV’s ULP design uses similar methods to the previously described iC-TW11 to reduce current consumption during active operation and in standby. However, the iC-PV has its own independent cycle and timing control to cyclically activate a defined measuring cycle without the need of an external microcontroller. Depending on the set sampling rate, revolutions can be counted at speeds from 12,000 to 100,000 rpm. The average current consumption ranges from only 2 µA to 30 µA allowing

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