Electrical noise near analog signals and measurement instrumentation often can cause symptoms including unexpected voltage spikes and ripple or jitter, causing incorrect or non-repeating readings. Pulse inputs generally have a very high impedance, making them susceptible to electrical noise. Because of the inherent sensitivity, loggers connected to external power supplies such as COBRA and WILD-M-R, can record false pulse counts in environments present with electrical noise.

Causes of False Input Data

Ground Loops

Electrical equipment such as electric motors can induce noise on power lines. This can cause a logger's power supply ground and the meter's ground to vary relative to each other.

Electromagnetic Induction

This happens when the pulse input cable to the logger is close to electrical noise EMF, e.g. the logger is situated close to power cables of other electrical equipment.

Factors that may contribute

Knowledge of the setup is required in order to determine what may be causing the erroneous pulse input data, however the below factors are common factors that may contribute.

• The logger and a flow meter are connected to the same power grid;
• The Power supply of a logger and a flow meter come from different locations in the power grid;
• High power equipment is connected to the power grid, e.g. electric motors.

Mitigation options

• Connect the power supply of the logger as close as possible to the flow meter's power supply
• Disconnect the flow meter or the logger from the power grid;
  • Use a Wasp logger instead of a Cobra logger, or
  • Use an external rechargeable battery (SLA) and a solar panel to charge the Cobra logger