Setting The Hi And Lo Alarms; Channel Scan - Lakeshore 818 User Manual

3.5.4

Setting the HI and LO Alarms

The alarms may be changed if the rear panel ALARM SET switch (Configuration DIP Switch 3) is ON (1). To
change the alarms from the front panel:
1. Turn ON (1) rear panel configuration DIP Switch 3, marked ALARM SET.
2. Press either the HI ALARM or LO ALARM key and check the displayed alarm setting. To change the
setting, push either the s or t key until the desired setting is reached. Note: the alarms can only be set in
temperature. If voltage is the display units, the display defaults to kelvin if an alarm key is pushed. The
alarm setpoint resolution is 0.1 K, °C or °F. The alarm setpoint is bounded by the sensor temperature
range listed in Table 3-1.
3. For the Model 819, press the CHANNEL key and the s or t key until the desired channel is reached,
then implement step 2.
4. The alarms take on the new values immediately. The ALARM SET switch only deactivates the ability to
set the alarms if it is in the OFF (0) position.
3.6 MODEL 819 CHANNEL SELECTION
The Model 819 has four sensor inputs (or channels) numbered 1 thru 4. To change the display input, press the
CHANNEL key and either the s or t key. The channel input position displays to the left of the display. Hold
the CHANNEL key for greater than one second to toggle the scan mode, and greater than two seconds to
display the dwell time for the selected channel.
3.6.1

Channel Scan

In hold mode, the Model 819 internally scans each channel and updates alarms approximately every
8 seconds. In scan mode, the Model 819 continuously monitors the displayed channel and updates its alarms
only. If a channel is excluded from the scan sequence (its dwell time is set to 0), the alarms of this channel are
not updated. To enable or disable the scan, hold the CHANNEL key in for greater than one second. The
Model 819 enters the SCAN mode as indicated by the SCAN annunciator.
3.6.2 Setting Channel Dwell Time
To set the dwell time for a given channel, hold in the CHANNEL key for greater than two seconds and use the
s or t keys to increment or decrement the dwell times between 0 (skip), 5, 10, 30 and 60 seconds. Next
increment the channel and repeat the dwell time setting process.
3-4
Lake Shore Model 818 / 819 Cryopump Monitor User's Manual
Operation