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Pomiar prądów faz silnika krokowego przez oscyloskop dwukanałowy


jak równocześnie oglądać wykresy prądów faz?...
trzeba jakoś oddzielić masy kanałów oscyloskopu (takiego tańszego bez separacji kanałów)...

gotowe sondy do separacji kanałów są DROGIE...

optoizolacja jest trudna do realizacji...

można próbować zastosować wzmacniacz operacyjny... w celu odsymetryzowania sygnału napięciowego z rezystora do pomiaru prądu fazy...


http://freecircuitdiagram.com/2010/10/02/differential-current-sensing-inside-h-bridge/

datasheet ad8205
http://www.autex.spb.ru/ad/AD8205.pdf

można zapewne próbować "obtanić" projekt przez zastosowanie normalnego wzmacniacza + rezystory o większej precyzji (tak jak to widać w datasheecie ad8205)

ciekawe czy można to zrobić inaczej?

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ISO122
Precision Lowest Cost
ISOLATION AMPLIFIER

FEATURES
100% TESTED FOR HIGH-VOLTAGE BREAKDOWN
RATED 1500Vrms
HIGH IMR: 140dB at 60Hz
BIPOLAR OPERATION: VO = ±10V
16-PIN PLASTIC DIP AND 28-LEAD SOIC
EASE OF USE: Fixed Unity Gain Configuration
0.020% max NONLINEARITY
±4.5V to ±18V SUPPLY RANGE

APPLICATIONS
INDUSTRIAL PROCESS CONTROL:
-Transducer Isolator, Isolator for Thermocouples,
-RTDs, Pressure Bridges, and
-Flow Meters, 4mA to 20mA Loop Isolation
GROUND LOOP ELIMINATION
MOTOR AND SCR CONTROL
POWER MONITORING
PC-BASED DATA ACQUISITION
TEST EQUIPMENT

DESCRIPTION
The ISO122 is a precision isolation amplifier incorporating a novel duty cycle modulation-demodulation technique. The signal is transmitted digitally across
a 2pF differential capacitive barrier. With digital modulation the barrier characteristics do not affect signal integrity, resulting in excellent reliability and good high frequency transient immunity across the barrier. Both barrier capacitors are imbedded in the plastic body of the package. The ISO122 is easy to use. No external components are required for operation. The key specifications are 0.020% max nonlinearity, 50kHz signal bandwidth, and 200mV/°C VOS drift. A power supply range of ±4.5V to ±18V and quiescent currents of ±5.0mA on VS1 and ±5.5mA on VS2 make these amplifiers ideal for a wide range of applications. The ISO122 is available in 16-pin plastic DIP and 28- lead plastic surface mount packages.

http://focus.ti.com/lit/ds/symlink/iso122.pdf

[markcomp]

Sensor interface DIL-16, UTI-DIL16


Universal Transducer Interface (UTI)
Revolution in Sensor Interfacing


Features
· Provides interfacing for many types of sensor
elements: capacitors, platinum resistors, thermistors, resistive bridges and potentiometers
· Measurement of multiple sensor elements
· Single 2.9 V - 5.5 V power supply, current consumption below 2.5 mA
· Resolution and linearity up to 14 bits and 13 bits
· Continuous auto-calibration of offset and gain
· Microcontroller-compatible output signal
· Tri-state output
· Typical measurement time 10 ms or 100 ms
· 2/3/4-wire measurement available for almost all measurements
· AC excitation voltage signal for all sensor elements
· Suppression of 50/60 Hz interference.
· Power down mode
· Temperature range -40ºC to 85ºC
· Die operating temperature up to 180ºC

1. General Description
The Universal Transducer Interface (UTI) is a complete analog front end for low frequency measurement applications, based on a period-modulated  oscillator. Sensing elements can be directly connected to the UTI without the need for extra electronics. Only a single reference element, of the same kind as the sensor, is required. The UTI outputs a microcontroller-compatible  period-modulated signal. The UTI can provide interfacing for:

· Capacitive sensors 0 - 2 pF, 0 -12 pF, variable range up to 300 pF
· Platinum resistors Pt100, Pt1000
· Thermistors 1 kW - 25 kW
· Resistive bridges 250 W - 10 kW with maximum imbalance +/- 4% or +/- 0.25%
· Potentiometers 1 kW - 50 kW
· Combinations of the above mentioned

The UTI is ideal for use in smart microcontroller-based systems. One output-data wire reduces the number of interconnect lines and reduces the number of optocouplers required in isolated systems. Continuous autocalibration of offset and gain of the complete system is performed by using the three-signal  technique. The lowfrequency interference is removed by using an advanced
chopping technique. The function selection can be configured in both software
and hardware.

https://www1.elfa.se/data1/wwwroot/assets/datasheets/07308836.pdf