Tips For Reducing Signal Interference - Tektronix ADA400A Instruction Manual

Tips for Reducing Signal Interference

Signal and Ground
Connections
ADA400A Differential Preamplifier
Differential Preamplifier allows you to select upper bandwidth limits of FULL
(1 MHz), 100 kHz, 3 kHz and 100 Hz.
Disruptive electrical interference or "noise" from sources near the test setup can
affect measurements. The effects become even more apparent when measuring
low-amplitude voltages.
The electric-power system, for example, generates a line frequency of 50 or
60 Hz and can couple electrical noise from other devices. Power switches or
switching devices generate power line spikes. Unshielded or poorly grounded
electric motors can generate disruptive transients. Power lines and transformers
create magnetic fields that can induce a disruptive voltage in wires or input leads
that are not properly twisted together.
Devices such as digital or microprocessor based systems can radiate signals that
sensitive electronic detectors or amplifiers can receive and amplify. Switch-mode
power supplies generate interference in the range of 20 to 100 kHz. Sources of
interference can include florescent lights, laser printers, monitors, CRTs, even
radio transmissions.
Proper setup of the ADA400A Differential Preamplifier minimizes or eliminates
signal interference in most cases. There are three important strategies to reducing
signal interference:
1. Use the proper signal and ground connections for the particular application.
2. Limit the bandwidth of the test setup.
3. Isolate or eliminate sources of signal interference.
The techniques for proper signal and ground connections involve limiting noise
to the input:
H Minimize length of input leads.
H Select input leads that have the same length and type of construction.
H Use shielded coaxial cable or "twisted-pair" leads on the inputs.
H Connect shield or ground leads close to signal source.
H Restrict movement of input leads.
H Eliminate ground loops.
H Reject common-mode noise by operating in differential mode.
Reference
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