I am trying to design a crane load (Weight) measuring unit using motor current measurement technique. For some reasons we can't use load cells here.
Part of schematic I have drawn here
- An air core current transformer is used here to convert current into a measurable voltage. I have measured using a DSO 1.4Vrms at no load & 2.1Vrms at full load of crane capacity across 220 ohms resistor. Voltage waveform is sine wave. Points 2 & 3 haven't been tested yet.
- A diode rectifier & a low pass filter will convert 50Hz AC into DC. Every crane will be calibrated using standard weights & ADC values will be stored in EEPROM of a micro-controller for ADC value to weight correlation. Linearity of filters & rectifiers won't hamper the accuracy.
- A 10 bit ADC with 4.096v internal reference voltage will convert this dc into a value which will be converted into appropriate load (wight) using values stored in EEPROM during calibration in point 1.
I need help in designing a level shift amplifier with following points in mind.
- Can convert 1.3v to 2.2v into 0 to 4.096v, non-inverting with minimum opamps (if possible, only 1).
- Use of trim pots-resistors combination is required to make finer adjustments at site.
- Only 5v VCC supply is available.
- If possible, merge 2nd order 5 to 10Hz low pass filter with it. This will chop off AC ripples & provide smooth DC in proportion to CT output voltage.
Even if you have a different approach to crane load (weight) measurement, please share.