Troubleshooting Noise in an
Electrochemical System with a Rotator
This document describes several common potential sources of noise in an electrochemical
rotator system and methods that can be used to attempt to reduce the noise.
Overview
Noise is a common problem for researchers working with electrochemical systems.
Unfortunately, noise is difficult to trace and eliminate since it can originate from many
different sources. The following document describes important steps designed to
reduce noise in an electrochemical rotator system. It is possible that even after
implementing all of the steps detailed in this document, noise may still remain because
of additional factors, such as other lab infrastructure or instrumentation. In cases that
the noise cannot be reduced to an acceptable level, the ultimate step may be to
enclose the rotator system in a Faraday cage.
Common Sources of Electrochemical Noise
1.1
Reference Electrode
Issues with the reference electrode will sometimes occur, causing noise. In order for
your potentiostat to function properly, there must be adequate ionic conductivity
between the electrolyte and the reference electrode. To test the reference electrode,
make sure that the reference electrode: 1) is in good contact with the electrolyte
solution and 2) has a low impedance connection. High impedance is often introduced
when the frit between the reference electrode and the solution is clogged, restricting
the ionic conductivity between the inner chamber of the reference electrode and the
electrolyte. High impedance is also encountered when the potentiostat has a poor
connection to the reference electrode, such as a rusty alligator clip. Note that for lowionic concentration solutions and non-aqueous solvents the solution impedance will
typically be intrinsically high.
One simple problem related to reference electrodes that can occur is the existence of
a small air bubble around the tip or frit where the reference electrode contacts the
electrolyte. This commonly occurs when placing the reference electrode into the
electrolyte quickly or when the reference electrode is inserted too vertically. It can also
be a particularly common issue if the reference electrode frit is either pushed up into
the tip slightly or eroded away, such that the bottom of the frit is no longer coplanar
with the small opening at the bottom of the reference electrode tip. This air bubble
prevents contact between the reference electrode’s internal solution and the
electrolyte, creating high impedance and noise. To fix this problem, either carefully
slide the reference electrode in and out of solution at an angle until the signal improves,
or use a pipette to place a drop of electrolyte directly onto the bottom frit area before
inserting the reference electrode into the cell. In this way, the tip and frit maintain
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contact with the electrolyte to ensure ionic conductivity between the reference
electrode and electrolyte.
An easy method of testing for problems related to high impedance is to switch the
existing reference electrode in the electrochemical system with another reference
electrode. If a second reference electrode is not available, a home-made Ag/AgCl
reference electrode can be readily constructed. To construct an Ag/AgCl reference
electrode, insert a Pt and an Ag wire (typically 0.5 mm to 2 mm in diameter) into a 1M
KCl solution. Connect the Pt wire to the negative terminal and the Ag wire to the
positive terminal of a 1.5 V battery. Maintain this electrode configuration for about 60
sec. Alternatively, a potentiostat can be used for this purpose. To use a potentiostat,
short the WKG and WKG-SENSE connections together and connect them to the Ag
wire; short the CTR and REF together and connect them to the Pt wire. Finally, setup an
electrolysis (chronoamperometry) experiment with an applied potential of 1.5 V for 60
sec. The constructed Ag/AgCl reference electrode can be used in a 100 mM KCl
electrolyte solution to test the electrochemical system. This in-situ reference electrode
does not suffer the frit problems that a normal glass reference electrode might
experience. If testing with the Ag/AgCl electrode eliminates the noise, this indicates the
original reference electrode is damaged and a new reference electrode is needed.
1.2
Cable Shielding and Length
Environmental noise can interfere with an electrochemical system through the cabling
between the potentiostat and the electrochemical cell. To reduce issues with noise
from this source, make sure that the cable connecting the potentiostat to the
electrochemical cell is as short as possible and/or that the cabling is shielded. Pine’s
WaveDriver bipotentiostat comes with a cell cable where all signal lines are individually
shielded. Additionally, Pine’s WaveNow and WaveNano potentiostats are equipped
with a standard cell cable (Pine Part#: AKCABLE5) that has all signal lines individually
shielded, and the signal lines are also shielded for Pine’s compact voltammetry cable
(Pine Part#: RRTPE04).
Pine’s CBP bipotentiostat has a shielded reference electrode (the outer conductor of
the BNC cable), but the working electrode(s) and counter electrode leads have
banana plug type connectors which are not shielded. However, the working
electrode(s) and counter electrode can be shielded by constructing a shielded cable
using a BNC patch cable and a two-banana-plug to BNC (female) adapter (Pine
Part#: EKX103). The ground from the two-banana-plug adapter should be connected
to the ground/shield on the reference electrode. Note that the shield for the reference
electrode can be used to shield the other electrode lines, but should not be connected
to any other metal or connectors. For example, it should not be connected to the silver
chassis ground.
1.3
Grounding the Rotator Motor Casing
In an electrochemical rotator system, the rotator motor is the main source of linefrequency noise (60 Hz). Motor noise can be effectively shielded (reduced) by
grounding the rotator motor. First, ensure that the rotator and rotator control unit share
a ground connection. Use a multimeter to measure the resistance between the
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support post of the rotator and the ground terminal on the front of the rotator control
unit. The resistance should be less than 1 Ohm. Next, attach the rotator control unit
ground to the chassis ground of the potentiostat. For Pine WaveDriver potentiostats, the
chassis ground is a silver socket on the back panel. The Pine CBP potentiostat’s chassis
ground is a silver socket on the front panel beneath the electrode connections. For
WaveNow potentiostats equipped with standard cabling (Pine Part#: AKCABLE5), the
black banana connector on the terminal end of the cable can be connected to the
chassis ground on the front panel of the rotator controller. Optionally, the rotator can
be grounded to the potentiostat (see: Figure 1). The metal post of the rotator may be
used as an attachment point.
Figure 1. Schematic of Grounding the Rotator to the Potentiostat.
1.4
Checking Rotator Brush Contacts
The brush contacts to the rotator shaft provide the conductive path to move electrical
signals to and from the working electrode (and ring where applicable) in the
electrochemical cell. Issues with these brush contacts are a possible source of noise.
Noise caused by the brush contacts to rotator shaft typically has a frequency
characteristic closely correlated with the rotator rotation speed. So, if changing the
rotator speed changes the observed noise, the brush contacts to the rotator shaft
should be examined. Open the clamshell doors on the rotator housing (see: Figure 2) to
inspect the rotator shaft and the brush contacts. The rotator shaft surface should be
very smooth and free of corrosion or defects. The brush contacts should be examined.
They should have either a flat smooth surface (when new) or a curved one that
matches the rotating shaft (after use). If the brush contacts are worn, the worn groove
should exactly match the curvature of the rotator shaft. If the alignment of the worn
Figure 2. Rotator Housing Closed and Open to Visualize Brush Contacts.
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groove does not match the curvature of the shaft exactly, do not try to align the
grooves by rotating the brush contact. This method is not accurate enough when done
manually. A slightly misaligned wear mark with respect to the shaft causes squeaking
and vibrations, which contribute to the recorded noise. If the brush contact groove has
already been misaligned, then remove the brush contact and polish out the previous
mark; or rotate the brush contact 90º with respect to the wear mark, so the new wear
mark will be perpendicular to the old one. Rotating the brush contact 90º can
eliminate the squeaking vibration. To polish the concave grooves from the brush
contacts, remove the brush rods from the rotator housing. The brush rods are threaded
into the housing and it should be possible to unscrew them by hand. Polish the brush
contact on a piece of sandpaper secured to a flat surface. Ensure that the brush rod is
perpendicular to the sandpaper. It is advantageous to hold the brush rod in a fixture,
such as the chuck of a drill press, to ensure it remains perpendicular to the sandpaper.
Brush contact rods should be replaced when the carbon portion is about to be worn
through. Replacement brush contacts can also be purchased. For MSR rotators, refer
to Pine Part#: ACAR063RM and for ASR rotators, Pine Part#: ACAR063RA.
Contact Us / Support
Please contact Pine with any of your needs: general and technical questions,
pricing/quotes, selection assistance, etc. You will always get a live person at Pine – no
calling tree. We are here to serve you.
Call +1 (919) 782-8320 Monday – Friday from 9 AM to 5 PM EST
Email the sales team at: pinewire@pineinst.com
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