ORP electrode maintenance is nothing more than occasionally cleaning the platinum surface with
a soft cloth and soapy water. You can use a very light abrasive, like 900-grit wet-and-dry
sandpaper, if the platinum is discolored. The important part of ORP maintenance is refilling the
reference electrode (see E10).
ORP uses a one point calibration:
1) Rinse your sensors several times with the ORP standard you’ll use for calibration.
2) Fill the calibration cup with enough standard to cover both the ORP and reference
electrodes.
3) Follow the Manta 2 Control Software calibration instructions.
E12 Depth and Vented Depth
Depth is measured by a strain-gauge transducer as hydrostatic water pressure. The deeper you
go in the water, the higher the pressure.
Depth sensors require no regular maintenance, but you might check occasionally to make sure
the pressure port (i.e. hole in the front of the sensor) is not clogged. If it is, don’t poke it with a
bent paper clip; call the factory for instructions.
Depth calibration is nothing more than “zeroing” the sensor in air, where one assumes the depth
to be zero:
1) Make sure the multiprobe is not in the water or in the storage cup as this will cause an
offset.
2) Expose the sensors to air.
3) Follow the Manta 2 Control Software’s calibration instructions.
Notice that the Depth sensor cannot distinguish between water pressure and the air pressure
over that water (i.e. barometric pressure). After you have zeroed the sensor, any change in
barometric pressure will be measured as a change in water pressure. Fortunately, water is
considerably heavier than air, so the error introduced by barometric pressure changes is small.
If that’s not good enough for you, there’s always Vented Depth. Vented Depth uses the same
transducer as does Depth, except that there’s a tiny hole in the back of the transducer. If you
have a vented cable (a cable that has a tube running through it), then atmospheric pressure is
sensed by the transducer via the little hole. Any change in barometric pressure will not affect the
depth reading.
Vented-Depth cables have a desiccant-filled housing at their surface end. The desiccant keeps
water from condensing in the vent tube. Keep that housing clean, and replace the desiccants
every year or so.
E13 Turbidity
Turbidity is measured as the fraction of an infrared light beam that is scattered at 90° to that
beam. More particles in the water mean more the light is scattered and so the Turbidity reading
is higher. Any material that accumulates on the optical surfaces of the Turbidity sensor is
indistinguishable from material in the water; that’s why most Turbidity sensors have little wipers to
clean the window(s).
Turbidity sensors require no regular maintenance, but you might check occasionally to make sure
the optical window (i.e. the little glass port on the front of the sensor) has not been damaged by
overzealous wiping.
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