A printing device is provided, which is configured to print a printing
fluid onto a printing medium. The printing device includes a printing
fluid reservoir configured to hold a volume of the printing fluid, a print
head assembly configured to transfer the printing fluid to the printing
medium, a conduit fluidically connecting the printing fluid reservoir to
the print head assembly, and a printing fluid detector associated with the
conduit. The printing fluid detector includes a first electrode and a
second electrode coupled with the conduit and configured to be in contact
with printing fluid in the conduit, a power supply configured to apply an
alternating supply signal to the first electrode, and detector circuitry
configured to detect a measured impedance value related to the presence of
printing fluid within the conduit by comparing the alternating supply
signal with a detected signal that has been modified from the applied
signal by an impedance characteristic of the printing fluid.
