#### hm_fa_da

##### Full Member level 5

in STPM10 datasheet it is mentioned dynamic range is 1000 and for current sensing inputs which are differential inputs, it says max voltage is +-0.3 V.

but it

__doesn't say anything about minimum__voltage, is the minimum input 0.3/1000=3mV ? it means it won't measure lower inputs ?

if i want to design a 5(100)A meter, which should be able to measure current from 20mA to 100A, so i can't use this chip ?

if i adjust the higher side on (100A) then the lowest side will be 0.1 A.

if i adjust the lower side on 0.02A then the highest side will be 20A !

are my calculations true ?!

if yes, i just saw a meter from a company which claims 5(100)A in specifications but uses STPM10 chip for ADC ... !

or Actaris ACE5000 which uses Cirrus CS5451 with 1000 dynamic range for 5(120) A.

according to IEEE62053-21(8.3.3) standard, the meter should be able to start metering from 0.004*Ib => 0.004*5A= 20mA . and maximum 120A.

can i manage this problem by changing gain by software ?

for example i choose a shunt to produce 3mV for 20mA, then the max would be 300mV for 20A, but when i get near 20A, i decrease gain, so i have room for higher currents ...

is this possible ?!

about the minimum differential input voltage, it is written in ATM90E26 datasheet only, it is written 5uV to 25mV ( dynamic range is 5000 )

other Metering ICs just say maximum input voltage ! ( like STPM10 )

i myself calculated the minimum input voltage according to dynamic range of each device.

Is there something wrong with my calculations ? i am confused !