ProMinent DULCOMETER Compact - Checkout Time for Measured Variable and Correction Variable; Checkout Time Control

10.6 Checkout time for measured variable and correction variable
Error text Description
LIMIT ERR Checkout time of the measured variable
TLIMITERR Checkout time of the correction variable
If upon the expiry of the checkout time, the valid measuring range is not reached, then
the DULCOMETER
®
Compact Controller exhibits the following behaviour:
n LIMIT ERR: The control is switched off. An error current is emitted, provided the
output is configured as a measured variable output
n TLIMITERR: The control is switched off. An error current is emitted, provided the
output is configured as a correction variable output or a measured variable output
Initially the transgression of a limit is only a limit value transgression. This leads to a
‘WARNING’ . Switching on the control time ‘TIMELIM’ (> 0 minutes), creates an alarm
from the limit value transgression. In the event of a [TLIMITERR] a, the control switches
to
[STOP] .
10.7 Checkout time control
Monitoring of the control path
The checkout time monitors the con‐
trol path. The checkout time mecha‐
nism permits detection of possible
defective sensors.
Dead time determination
Each control path has a dead time. The
dead time is the time, which the control
path requires to detect a change or addi‐
tion of metered chemicals using its own
instrumentation.
You must select the checkout time so that
it is greater than the dead time. You can
determine the dead time, by operating the
metering pump in manual mode and, for
example, dosing acid.
NOTICE!
Dead time determination
You should only determine the dead
time if the current process cannot be
negatively influenced by the manual
metering.
You must determine the time, which the
control path (i.e. the entirety of controllers,
sensors, measurement water, flow
gauges, etc.) requires to detect a first
change in the measured value starting
from the beginning of dosing. This time is
the
‘dead time’ . A safety margin, e.g.
25%, must be added to this dead time.
You must allocate an appropriate safety
margin for your own particular process.
The parameter
‘LIMIT’ can be used to set
a limit for the control variable. If the con‐
trol variable exceeds this limit value, the
CHECKTIME fault is triggered (checkout
time of the control has elapsed). The con‐
trol is switched to basic load and a fault
current output.
Control parameters and functions
84