Some may tell you that a Gamry Potentiostat is noisy because it's installed inside a noisy computer.Here's why they're wrong.
|
||
| The
Bottom Line |
||
| Gamry’s specification for
“Noise and Ripple” of the applied potential for the PCI4/300,
PCI4/750, and FAS2 Potentiostats is 20 µV(microVolts)
rms (1 Hz – 10 kHz). We guarantee
this specification for our Potentiostats in any Windows-compatible
computer. Compare this value to the
noise specification for any other commercial potentiostat.
Our search found no instrument whose noise specification matched or
exceeded Gamry’s! |
||
| Technical
Details |
||
|
In the lore of scientific instruments, a computer is considered to be electronically noisy. If that is true, then it seems counter-intuitive to expect a potentiostat that is installed inside a computer to exhibit low noise. How does Gamry do it? Is a
computer noisy? Yes, a
computer has very high noise levels inside its cabinet.
A computer is a digital device, which generates both magnetic and
electric fields as its internal signals switch.
These fields can couple noise into analog circuits.
However (and this is important) the noise in a computer occurs at very
high frequencies, typically greater than 100 MHz.
These frequencies are far higher than the frequencies that are important
to electrochemistry. Grounding.
The Gamry Potentiostat uses optical couplers to electrically
isolate the analog potentiostat from the earth ground of the computer in which
it is installed. Large AC currents
flowing through the computer’s ground would otherwise create noise in the
potentiostat. Filters.
The Gamry Potentiostat contains three analog filters at 5 Hz, 1000
Hz, and 200 kHz. One of these
filters is always active, discriminating against the computer’s high frequency
noise. Shielding.
If you examine a Gamry Potentiostat, you’ll see a big sheet of metal
that completely covers the analog components of the Potentiostat. This is a shield that protects the Potentiostat from
electrostatic pickup of computer noise. What
about the other guys?
If Gamry’s noise spec is 20 µV
rms, shouldn’t other manufacturers have an even lower noise spec?
After all, their potentiostat is not inside the computer.
It turns out that the greatest source of noise for a potentiostat that is
connected to the power grid through a receptacle in the wall is the 50 Hz or 60
Hz signal from the mains. AC power
voltage presents two problems: (1)
its amplitude is very large, either 110 or 220 volts, and (2) it is at a
frequency that is of interest to the electrochemist, so filtering is difficult.
Noise may be obvious at the mains frequency or at some harmonic, e.g.,
120 Hz or 180 Hz. Since
we’re on the subject, what does “Noise and Ripple” really mean?
For a Gamry Potentiostat, the noise level that will be
observed on the applied potential is less than 20 µV
rms (root mean square). To convert
rms to peak-to-peak, multiply by 1.414 (square root of 2) to convert to a peak
signal, then multiply by 2 to convert to peak-to-peak.
|
||
If someone tells you something negative about Gamry,
it's a good idea to call and ask us for our comments.
|
||
|
Last revised on Monday, October 30, 2006
|
||