Hello TI-Experts,
we are working on the evaluation of the PGA970 with a 3-wire half-bridge setup with PGA970EVM. Without the use of the external amplifier circuit on primary side and the RC circuit on secondary side, it seems to be ok. If the core of the inductive sensor is in the middle, then the measured amplitude at the center tap is half the amplitude of the excitation waveform (S1P/ADC1: Excitation waveform and S2P/ADC2: Center tap). But if we use the external amplifier circuit on primary side and the RC circuit on the secondary side to attenuate the signal, the behavior of the circuit changes.
- The PGA970EVM User's Guide says at 3.1: "A resistor divider is created with the internal impedance of these pins, allowing the return signal to be within a measurable amplitude of the ADC"..... => What is the value of the internal impedance at these pins?
- The use of the RC circuit on the secondary side should not affect the basic behavior of the circuit (just attenuate the signal), right? (1) If we connect the center tap to S2P the amplitude of the excitation waveform (measured at S1P) changes. Is there an explanation for this behavior? (2) Also, the measured amplitude at S1P changes depending on the positon of the sensor core (the measured excitation waveform should remain stable?). The ratio of the two amplitudes also changes (in the middle position the ratio should be 0.5?) We can't detect these behavior if we don't use the external RC circuits. How to deal with it? Any ideas? I attached a screenshot...
- We use a sensor with a measuring range of +- 1mm and a sensitivity of 73,5 mV/V/mm. Is it even possible to measure with a repeatable accuracy of about 1um? It appears difficult with respect to the adc range of 0V to 2.5V, an excitation waveform amplitude of about 1 Vp and the resulting sensitivtiy of 0,0735 mV/V/um considering noise etc. . What is the best way to achieve the highest possible accuracy?
- Is it possible to operate several sensors (3-Wire setup) with one PGA970 (Multiplexing)?
Sorry for asking that many questions.
Thank you in advance. Best regards.
