Screening, Grounding and Low Noise Instrumentation
EMI shielding box screening the potentiostat
BNC connectors used to screen inputs and outputs
Screened D-Type with screened multicore cable
The majority of noise affecting the final electrochemical measurements made comes from Electromagnetic Radiation from the environment. Most of this is from the mains ac power used in the laboratory, factory or hospital. Therefore it is essential to shield the potentiostat from this interferance by correctly screening the electronic circuitry and the cable and leads going to the electrode cell as well as the electrode cell itself. In the instrument this can be accomplished by using metal enclosures or special EMI boxes surrounding the potentiostat circuits. Leads to the electrode cell can be coax cable with bnc connectors or screened multicore cable with metal cased d-type connectors.
Ground connection to manually connect to Earth
Using USB connector to groung potentiostat
Using mains power supply to earth potentiostat
If the potentiostat is correctly shielded, the screening must be connected to a good ground or earth. Ideally this should be the building or power ground. This can be accomplished by connecting a ground socket to the power ground, connecting the potentiostat ground to the the usb port of a mains powered PC or using the earth of the power supply directly.
Smoothing and Filtering
As much of the noise as possible should be removed from the signal by correct shielding and grounding. After this, various methods of smoothing or filtering the signal can be used. Analogue smoothing can be designed into the potentiostat circuit in a number of locations. The signal from the potentiostat circuit can be fed into specially designed filter circuits with various cut-off frequencies to further process the signal. Finally various software filtering techniques can de used to reduce the final noise. With all these methods care must be taken to ensure that only the noise is removed and that the signal still contains the data and peaks wanted.
A second source of noise in potentiostat measurements may be caused by noise from the power supply source. In most cases, use of an isolated mains plug-in power supply will lead to low noise measurements. These supplies can also include a connection to the building earth to allow efficient screening of the potentiostat. In cases where extremely low noise is required, for instance with ultra low current potentiostats, rechargeable batteries can be used. Use of USB cables to provide power for the potentiostat is not recommended.