External Functions - Hanna Instruments HI 23 Series Instruction Manual

WATCHDOG

EXTERNAL FUNCTIONS

HOLD FUNCTION
PRESETTABLE TIMER (CLEANING FUNCTION)
When a dead loop condition is detected a reset is automati-
cally invoked.
The effectiveness of watchdog capability can be tested through
one of the special setup items. This test consists of executing
a dummy dead loop that causes watchdog reset signal to be
generated.
This function allows to perform the mainte-
nance procedures. When the relevant digital
insulated input (terminals #11 on page 8) is
on, the analog output is frozen at its last value
and the control and alarm relays are dis-
abled. The "Hld" indication is displayed on the secondary
LCD when the function is active. A 5 to 24 VDC voltage can
be applied to this input.
While in hold state, it is possible to display
the temperature reading on the secondary
LCD pressing the right arrow key. Only when
the key is released, the secondary LCD re-
turns automatically after a few seconds to
the "Hld" indication.
A timer is presettable by software to close a
digital insulated contact (terminals #12 on
page 8) after a user programmable time in-
terval with a minimum interval of 1 day (e.g.
for probe cleaning function). The time inter-
val is programmable in number of days through setup code
72.
This output is ON for the period set through setup code 77
(this period can be also changed when the output is ON).
The starting time of the cleaning timer can be set through
setup codes 73, 74, 75 and 76.
45