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The
Fail Safe
feature protects the process against critical errors arising from power
interruptions, surges and human errors. This sophisticated yet easy-to-use system
resolves these predicaments on two fronts: hardware and software. To eliminate problems
of blackout and line failure, the alarm function operates in a “Normally Closed” state
and hence alarm is triggered if the wires are tripped, or
when the power is down. This is an important feature
since with most meters the alarm terminals close only
when an abnormal situation arises, however, due to line
interruption, no alarm is sounded, causing extensive
damage. On the other hand, software is employed to set
off the alarm in abnormal circumstances, for example,
if the dosing terminals are closed for too long a period.
In both cases, the red LED’s will also provide a visual
warning signal.
The Fail Safe mode is accomplished by connecting the external alarm circuit between
the FS•C (Normally Open) and the COM terminals. This way, an alarm will warn the
user when EC exceeds the alarm thresholds, during power down and in the case of a
broken wire between the process meter and the external alarm circuit.
Note
In order to have the Fail Safe feature activated, an external power supply has to be
connected to the alarm device.
CONTROL THROUGH ANALOG OUTPUT
Models
HI700221
and
HI710221
have a proportional analog signal (selectable
among 0-1mA, 0-20mA, 4-20mA, 0-5VDC, 1-5VDC and 0-10VDC) at the analog output
terminals. With this output, the actual output level amplitude is varied, rather than the
proportion of ON and OFF times (duty cycle control). A device with analog input (e.g. a
pump with a 4-20 mA input) can be connected to these terminals.
