The work of the measuring chip needs a clock, and the crystal oscillator provides the working clock for the measuring chip.
Digital circuits are mainly divided into two types of circuits, logic circuits and timing circuits, logic circuits do not need a clock, timing circuits need a clock, many chips contain more complex timing circuits, need to have a clock to work normally.
Some devices have a built-in RC oscillator and do not require an external clock. However, the energy metering chip generally needs to output counting pulse, the precision of the pulse is higher, the accuracy of the ordinary RC oscillator can not meet the requirements, so the external crystal oscillator is used to provide the clock.