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I have a charge-mode piezoelectric dynamic pressure sensor (datasheet link) that I want to read a signal from. If you look at the datasheet it says the sensor outputs are in a balanced and floating configuration, which I think means its output is a differential signal. Since it is a charge mode device, I will need to use a special charge amplifier to condition the signal to a low impedence voltage mode signal.

So I have two question related to this topic:

  1. Is there any reason why I can't or shouldn't treat the output of this charge-mode sensor as a single-ended signal by tying the negative pin to ground? This would allow me to use a coaxial cable for the connection between the sensor and my charge amplifier. The charge amplifier that I currently have is only meant for RSE signals, so it's input connector is BNC.

  2. Are there any benefits to using a differential signal over a balanced line rather than a single ended signal running over shielded coax?

This sensor will be operating right next to a DC generator, so it will be an electrically noisy environment.

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  • \$\begingroup\$ Page 7 of this app note talks about some of the benefits of differential signaling. They mention that it eliminates the effects of capacitive coupling onto one of the signal lines, but it seems like you wouldn't get that with shielded coax. \$\endgroup\$ – Ryan Helminen May 9 '13 at 13:36
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You achieve the best shielding if you connect the shield to the case on both sides of the cable.

Ground currents between device and sensor grounds produces voltage on the shield resistance/impedance. This voltage will add to your measurement, if you use shield as one of the wires.

Even if you isolate the coax ground from sensor ground it will have a slight capacitive coupling. All depends on your environment and requested accuracy.

Problems disappear for high frequencies (>1MHz for 10m cable), where coupling between shield and core acts as a common mode filter / transformer.

for best results:

low frequency - use twisted pair, shielded

high frequency - you may also use coax if low frequency is removed

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  • \$\begingroup\$ -1: Shielding should be DC connected to case or ground only at one end, and at most, AC coupled at the other end. There have been multiple questions on this site, as well as app notes by several manufacturers, that explain why. \$\endgroup\$ – Anindo Ghosh Jul 22 '13 at 5:53

protected by W5VO May 9 '13 at 1:11

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