21
Operation
The TDS multiplier is highly dependent on the nature of the ionic species
present in the water sample. To be assured of moderate accuracy for
the conversion, you must determine a multiplier for the water at your
sampling site. Use the following procedure to determine the multiplier for
a specific sample:
1.
Determine the specific conductance of a water sample from the
site.
2.
Filter a portion of water from the site.
3.
Carefully measure a volume of the filtered water. Completely
evaporate to yield a dry solid.
4.
Accurately weigh the remaining solid.
5.
Divide the weight of the solid (in grams) by the volume of water
used (in liters) to yield the TDS value in g/L for the site.
6.
Divide the TDS value in g/L by the specific conductance of the
water in mS/cm to yield the conversion multiplier.
NOTE:
If the nature of the ionic species at the site changes
between sampling studies, the TDS values will be in
error. TDS cannot be calculated accurately from specific
conductance unless the make-up of the chemical species in
the water remains constant.
Setup Depth
→
Setup
→
Depth
Cable assemblies with a depth sensor in the bulkhead can measure virtual
vented depth. The virtual vented depth measurement allows for real time
compensation for atmospheric pressure using the handheld’s barometer.
Depth offset
: Depth offset can be used if referencing water elevation
against a known value. If a depth offset is entered (in meters), the output
value will shift by the value of the offset (
Figure 28
).
A common offset entered by the user is the depth sensor location relative
to the rest of the WQ sensors. This value is 0.272 m on the 4-port cable
(
Figure 29
).
Altitude/Latitude
: To compensate for atmospheric pressure based on
elevation and gravitational pull, enter the local altitude in meters relative
to sea level and latitude in degrees where the instrument is sampling.
Latitude effect: Varying latitudes can cause up to a 200 mm change in
depth from equator to pole.
Altitude effect: A 100 m change in altitutde causes a 1.08 mm of change
to the depth readings.
Figure 28
Setup Depth
Figure 29
Distance of depth sensor to
WQ sensors on 4-port cable
Setup Conductivity
(continued)
Depth
Sensor
0.2
72
m
WQ
Sensors
