INSTRUMENT MANUAL
VACUUM GAUGE MODEL MM200
160Phone:(215) 947-2500 fax:(215) 947-7464 e-mail:sales@televac.com web site:www.televac.com
MM-200_im REV M
Page 44 of 160
TELEVAC
RANGE OF USE
For relays assigned to the following types of sensors:
Cold Cathode - any value up to 10
-2
Torr
Convection - 1 micron to 990 Torr
Diaphragm - 1 to 990 Torr
Hot Cathode - any value up to 10
-2
Torr
Thermocouple - 1 micron to 3 Torr.
Settings above 3 Torr, if required, will have to be set experimentally and will differ depending on whether
the pressure is increasing or decreasing.
CHANGING SENSOR ASSIGNMENT
When changing sensor assignment TO A DIFFERENT TYPE OF SENSOR the following step must be taken to
assure proper operation:
Use the DOWN ARROW to RUN THE SET POINT TO ZERO BEFORE RESETTING IT to the desired setpoint.
Example 1: Controlling a Cross-over Valve.
Cross-over is the point at which the high vacuum pump (e.g., diffusion pump) is connected to
the vacuum system. This is usually done automatically at a pressure in the range of 80 to
100 microns.
Relay 1 is set to energize at a pressure of 80 microns on the signal from thermocouple sensor
#1, which monitors the pressure in the main chamber. When the pressure drops below 80
microns, a sequence of steps is initiated by the change in status of the relay, namely:
The roughing valve is closed, then the foreline is opened and then the large main valve is
opened. This connects the high vacuum pump directly to the vacuum chamber and allows
the high vacuum pumping to proceed.
A different upper and lower setpoint are programmed. While the system is pumping down, the
relay does not change its state until the pressure falls below the lower setpoint and does not
revert back to its normal position until the pressure rises above the upper setpoint.
Example 2: Pressure Control
The relay is set up in a similar manner in this example. In this case, the relay controls a valve
on a gas inlet line to roughly control the system pressure between 1 and 4 Torr.