A-11
Appendix A Maintenance and Troubleshooting of this Device
A2-4-7 Clogging simulation test cannot be conducted.
When the clogging simulation test cannot be conducted, only the index value data under normal
operating conditions (index values collected in section A2-4-2) can be used to determine the
threshold value.
When many index values can be collected, calculate the average value (μ) and standard deviation
(σ), and determine the threshold value based on μ ± nσ. To eliminate misinformation, a value from
4 to 6 is recommended for n.
The threshold value can also be determined using the maximum (xmax) and minimum (xmin)
index values. For example, the threshold value should be set to a value that is no more than (xmax−
xmin)/2 from the minimum value, as shown in the figure below.
max
Threshold
value(Low)
Index value range
under the normal
operating conditions
Note that the threshold value determined using only the index value data under normal operating
conditions is not always appropriate. The index value may become smaller than the threshold value
due to causes other than clogging, or the index value may not become smaller than the threshold
value even when clogging occurs. Observe changes in the index value for a short period after the
threshold value has been determined, and then check that the index value does not become smaller
than the threshold value under normal operating conditions, and that the difference between the
correct value range and threshold value is not large. Revise the threshold value when necessary.
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