Method and apparatus for electrode impedance measurement

A method of obtaining a measure of electrical impedance in respect of one or more sensing electrodes of an electromagnetic flowmeter, the method comprising:

• injecting intermittent impedance measurement pulses to at least one of the sensing electrodes whilst subjecting the sensing electrodes to a cyclically varying electromagnetic field, thereby causing the sensing electrodes to produce a composite signal comprising electromagnetically induced flow measurement signals and electrode impedance measurement signals;
• and
• subjecting the composite signal to a filter operation in which the composite signal is combined with a delayed portion of itself, the delay period being such as to cancel the electromagnetically induced flow measurement signals from the composite signal, thereby enabling the electrode impedance measurement signals to be extracted and used to obtain a measure of electrode impedance.

A sensing apparatus for obtaining a measure of electrical impedance in respect of one or more sensing electrodes of an electromagnetic flowmeter, the sensing apparatus comprising:

• one or more signal generators configured to intermittently inject impedance measurement pulses to at least one of the sensing electrodes whilst the sensing electrodes are subjected to a cyclically varying electromagnetic field, thereby causing the sensing electrodes to produce a composite signal comprising electromagnetically induced flow measurement signals and electrode impedance measurement signals;
• and
• filter circuitry configured to combine the composite signal with a delayed portion of itself, the delay period being such as to cancel the electromagnetically induced flow measurement signals from the composite signal, thereby enabling the electrode impedance measurement signals to be extracted and used to obtain a measure of electrode impedance.