Hach ORBISPHERE 51 Serie Manuel D'utilisation Simplifié page 19

Option
Display
resolution:
Thermal cutoff:
2. TC sensor
The measurement configuration for a TC sensor is the same as for an EC sensor with the
addition of one extra selection criteria:
• Purge gas: From the drop-down list, select the purge gas being used for the TC sensor.
7.3.3 Measurement alarms configuration
Set the thresholds for the low/high concentration levels according to the application.
1. Select the Alarms button on the Measurement configuration screen:
Option Description
Low Low 2nd stage for too low concentration alarm.
Low 1st stage for too low concentration alarm.
High 1st stage for too high concentration alarm.
High High 2nd stage for too high concentration alarm.
Hysteresis The hysteresis is used to prevent relay flickering when the measurement is just at the alarm
levels. Set this to a minimum but enough to eliminate flickering. For example, if the High Alarm
is set to 40 ppb and the Hysteresis is set to 10% then the High Alarm is activated once the
measurement reaches 40 ppb but only deactivated once it drops below 36 ppb. With the Low
Alarm the opposite is true in that if the Low Alarm is set to 20 ppb and the Hysteresis set to 10%
then the Low Alarm is activated when the measurement drops below 20 ppb and deactivated
when it rises above 22 ppb.
Delay The delay in seconds, before alarms go on whenever concentration values go above "High
alarms" or below "Low alarms". Set this to a minimum value, but enough to avoid alarms for
non-representative peaks beyond the set level.
7.3.4 Measurement filter configuration
The filters are aimed at "flattening" the measurement curve in situations where the process shows
atypical peak values that could otherwise hamper the interpretation of measurement readings. The
filter is applied on the last set of measurements each time a measurement is taken.
1. Select the Filter button on the Measurement configuration screen:
Option Description
State Set the filters to Enabled or Disabled.
Type If enabled set the filter to Mean or Median.
Mean is the mathematical average of the last set (depth) of measurement values.
Median allows for eliminating atypical peak measurement values and averaging the
remaining ones. The calculation sorts the last measurement set (depth) by values, then
ignores the highest and lowest values and averages the remaining values (central depth).
Description
Maximum resolution depends on gas, membrane and unit. A maximum of 5 digits can be
displayed. Decimals can be limited to 0, 1, 2 or 3 decimals for easier reading. That does
not affect the actual resolution of data measured and stored, but only the data displayed.
To protect the sensor, the thermal cutoff function allows for setting a sample high
temperature limit. If exceeded (during a Cleaning In Place cycle for example) the
electrical signal to the sensor is cut off, the measurement session is suspended and the
system displays a HOT alarm message. The system resumes when temperature drops
to 90% of the specified cutoff temperature.
• Thermal cut off options: Disabled / enabled.
• Thermal cut off temperature: To be set according to conditions.
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