Tips to Reduce Noise Part 3
: When AC noise is coupled into the circuit/wire via a parasitic capacitor through the air.
This most commonly occurrs with fluorescent lights, switching power supplies, or other common electronics in the lab. Electrostatic noise is generated by the presence of a voltage with or without current flow (turning “off” vs unplug/remove).
Schematic of Electrostatic-Noise Coupling:
This conduction path takes the path of the parasitic capacitor that exists between every body/object. The size of the capacitor is usually about .5 picofarads. The conduction path is frequency dependant.
Xc = 1 / 2 Pi F C
Simple voltage divider calculations Vout = Vin ( R2 / (R1 + R2))
Real World Example
V noise@tether = 220 * 20K / ( 1/ (2 pi F C))
= 220 * 20K * 2pi 50hz .5 pf
= 220 * 20K / 1 / (6.28 * 50 * .5 E-12)
= 690 microvolts
The picture above demonstrates how electrostatic noise can effect the signal of interest.
The easiest and most effective method of removing electrostatic noise is to physically remove/distance the noise emitting device from the recording setup. In certain experimental situations some factors may require the device to be close to the recording setup so an alternative solution must be found.
Shielding provides this solution. It functions by capturing the charges that would normally pollute the signal. Once collected, the charges must be drained off to a reference potential (Panel Ground). The image shown below is that of the HS-18 with a Litz tether (shielded). Neuralynx offers this Litz tether in both shielded and unshielded versions. Mass of tether in both shielded and unshielded versions: 104mg/cm and 74mg/cm respectively.
: The standard configuration includes an Omnetics board connector, a µDB37M connector, optional LEDs, with a 3m Litz wire.
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