Hach AutoCAT 9000 - Maintenance; 9.1 General Instrument Care

Below Detectable Limit
50081_BDL.fm Page 137
Below Detectable Limit
Method Limits
When a titration result is below the limits of the Hach method in use, the instrument
will return a result of “Below Detectable Limit” (BDL). During normal operation, drift
can occur. Even when a result reads below the method threshold, a real endpoint with
low noise level is possible.
The BDL feature allows for review of the titration curve for a usable endpoint.
Example 1 shows a BDL result with a high level of noise and no clear endpoint.
Example 2 shows a BDL result with usable data (low noise and a sharp endpoint).
Example 1 Example 2
1. Press DEL to view the
titration curve.
2. Press the CHECK MARK
to accept BDL as the result.
3. In this example, “Below
Detectable Limit” is stored
with Test 1 for Sample 1.
1. Press DEL to view the
titration curve.
Example 2, continued
2. Press DEL to perform
manual endpoint
determination.
3. Use the navigation keys
to select two line segments,
one on each side of the
titration end point. Position
the vertical lines (cursors) at
the beginning and end of
each segment.
Press the
CHECK MARK to
confirm changes or press
DEL to return to the Zoom
window.
4. Press the CHECK MARK
to accept this calculated
result, press
DEL to return to
the previous window to
adjust the linear segments
and analyze the data again.
5. If the results are not
usable, press
DEL twice to
return to the initial Zoom
Range Determination
screen. Press the
CHECK MARK to accept
BDL.