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1.1
GENERAL
The information contained in this manual pertains to the installation, operation, remote programming, options
and accessories and calibration procedures for the Lake Shore Cryotronics, Inc. Model 818 and 819
Cryopump Monitors and the Balzers TMU-121 Cryopump Monitor.
NOTE: The TMU-121 is identical to the Model 818 except for the addition of a back panel keylock switch.
Users may wire two silicone diode sensors directly to the TMU-121; the keylock switch selects which input to
display. All other front panel and RS-232 operation is identical to the Model 818.
1.2
DESCRIPTION
The Model 818/819 is a microprocessor controlled instrument which provides direct digital display of
temperature with up to 4 digits of resolution in K, °C or °F and sensor voltage to 1 mV.
The Model 818 features one input with two alarms. The alarms can be used to safeguard or initiate and control
automatic cryopump regeneration cycles. The alarms are configured as HI and ID alarms. Set alarm setpoints
from the front panel with function keys and up/down keys, or simply check them without changing their values.
The alarm setpoint resolution is 0.1 K, °C or °F over the sensor temperature range. Table 3-1 describes
sensor temperature ranges. For security, the up/down keys can be deactivated by a rear panel DIP switch.
A deadband around each setpoint reduces or eliminates relay contact chattering.
The Model 819 features four inputs with two alarms (as described above) for each input. The Model 819 can
also scan between channels with dwell times of 0 (skip), 5, 10, 30 or 60 seconds for each channel.
The Model 818/819 directly reads temperature from Lake Shore DT-470 or DT-500 Series Temperature
Sensors. All DT-470 sensors follow the same temperature response curve and come in four bands of tracking.
Low temperature (2 to 100K) accuracies range from 0.25K for band 11 to 1K for band 13. The units have a
specified temperature range of 4 to 475 K with DT-470 sensors and 4 to 325 K with DT-500 sensors.
Diode sensor voltages are digitized with a resolution of 100 mV out of 3 volts full scale. The accuracy of the
electronics with DT-470 sensors is better than ±0.01 K below 28K and ±0.1K above 28K. The equivalent
display temperature rounds to 0.1 above 100 (any units) and 0.01 below 100.
The Model 818/819 features an RS-232C Serial Interface which allows users to monitor temperature, and
monitor and change alarm setpoints from a host computer. Sensor input(s), alarm contacts, and RS-232C
lines are located on the instrument rear panel.
Introduction
Lake Shore Model 818 / 819 Cryopump Monitor User's Manual
CHAPTER 1
INTRODUCTION
1-1
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