Lake Shore Model 218 Temperature Monitor User’s Manual
Operation
4-13
4.8.1 Example of Low and High Analog Parameter Setting
With the analog output set to input mode, the temperature input data and voltage output data can be
related as shown in the top diagram. This setup results in a wide temperature range but sensitivity is
poor. The resulting sensitivity is 0.01 V/K or 10 mV/K.
If the application does not require a wide temperature range, the user can change the value of the low
and high parameters to improve sensitivity. The bottom diagram shows how sensitivity improves
when working at liquid nitrogen temperature (77 K). This setup has a narrow range with much
improved sensitivity of 0.2 V/K or 200 mV/K. Please note that in any application, the resolution of the
analog output voltage is always 1.25 mV as specified.
C-218-4-3.bmp
Figure 4-3. Example of Low and High Analog Parameter Setting
4.9 ALARMS SETUP AND OPERATION
Each input of the Model 218 has high and low alarm capability. Input reading data from any source can
be compared to the alarm setpoint values. A reading higher than the high setpoint triggers the high
alarm for that input. A reading lower than the low alarm setpoint triggers the low alarm for that input.
If an alarm activates for a particular input, the display location for that input flashes. The beeper inside
the instrument can also be programmed to sound if any alarms activate. The eight relays on a 218S can
also be tied to alarm functions as described in Paragraph 4.11.
The system Alarm annunciator steadily displays when any alarm is enabled; it flashes when any alarm
activates. An input need not display for the system Alarm annunciator to indicate input alarm status.
Latching Alarms
. Often used to detect faults in a system or experiment that require operator
intervention. The alarm state remains visible to the operator for diagnostics even if the alarm condition
is removed. Relays often signal remote monitors or for added safety take critical equipment off line.
Alarm Reset clears latched alarms.
Non-Latching Alarms
. Often tied to relay operation to control part of a system or experiment. The
dead band parameter can prevent relays from turning on and off repeatedly when the sensor input
reading is near an alarm setpoint.
Example:
If the high alarm setpoint = 100 K and the dead band = 1
K, the high alarm triggers when sensor input temperature increases to 100 K, and it will not deactivate
until temperature drops to 99 K.
To begin alarm setup, press
Alarm Setup
. The first display appears. Use the Data Selection keys to
cycle through the inputs (1-8) to set up for alarms. Press
Enter
when the desired input appears.
The second display in the setting sequence appears. Use the Data Selection keys to turn alarm
operation On or Off for the selected input.
Off
Disables alarm operation for the selected input. The instrument skips to the eighth display
screen below.
On
Enables alarm operation for the selected input and displays the third display in the setting
sequence.
