www.miinet.com
Moore Industries-International, Inc.
- 33 -
User’s Manual
224-790-00K
May 2018
Programmable Limit Alarm Trips
SPA
2
SECTION 4
must be done on a regularly scheduled basis, both with near-end and far-end open circuits on each
of the wires.
Leakage current into a broken wire can prevent the voltage from dropping to the broken wire
threshold. For example, on a 1-5V input, with a broken wire threshold of 0.6V, a leakage current
of 1microamp into the broken wire will hold the input voltage at approximately 1.1V indefinitely. No
alarm results under these conditions.
If the external wiring is long and has significant capacitance, broken wire response time is slowed
by the RC time constant of the SPA
2
input resistance and the external wire capacitance. For
example, 1 km of wire with 100pf/m capacitance and a far-end break, has a capacitance of
0.1microfarad. The time constant will be 0.11 seconds. Using a starting voltage of 3V and a broken
wire threshold of 0.6V, the threshold is reached in approximately 0.18 seconds. The instrument
response time must be added to this time.
If both leakage and capacitance exist, the time to threshold can extend greatly. Using a 5V starting
voltage, 0.6V threshold voltage, 1 km of wire and 0.5 microamps leakage current, the threshold is
reached in 0.42 seconds. The instrument response time must then be added to this time.
8. “SCALE MODE” appears; press
SELECT
. Choose whether or not to enable scaling. This will
be configured in the next menu. Select “SCALE OFF” or “SCALE ON” and press
SELECT.
Caution:
Turning on scaling will disable custom-curve and turning off scaling will not restore
custom-curve. The custom-curve can only be restored using the PC configuration Software. The
custom data points will remain unchanged.
Scale Mode–
This allows you to customize your display for your application. By example: if
your process is sending a 4-20mA signal to the SPA
2
and you wish to view the input as
0-100% then this can be accomplished with the Scale Mode feature.
9. “EXIT OPTNS” (Exit Options) appears. Press
SELECT
. Proceed to the “SCALE INPUT”
menu.
