INSTRUMENT MANUAL
VACUUM GAUGE MODEL MM200
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MM-200_im REV M
Page 148 of 160
TELEVAC
Cold cathode gauges have jumpers on the PC board so that the following selections can be made for control by
thermocouple or convection type gauges:
1. Analog
2. MPI
3. MPI#2
4. None
If any cold cathode gauges are installed, the following scheme is employed so that their operation may be
controlled by associated thermocouple or convection type gauges:
1. The "Analog" selection would not normally be used with the model MM200. It is included for use when the
board is installed in an analog MA200 unit. However, it can also be used in a microprocessor unit if desired. The
analog selection allows selection of any other sensor to control the on-off operation of the cold cathode. The
controlling station is selected by jumpers on the cold cathode PC board. The jumper that is normally in the "MP"
position is moved to make this selection. The set point is manually set using a potentiometer on the cold cathode
PC board. The comparison is made between the raw signal (not linearized) from the selected sensor, and the
potentiometer setting. The controlling sensor would normally be any thermocouple or convection type sensor. A
hot cathode sensor should never be chosen for the controlling sensor.
2. MPI can be selected with the jumper, in which case, the lowest station number thermocouple or convection
type gauge controls the on-off operation of the cold cathode gauge.
3. MPI#2 can be selected with the jumper, in which case, the next lowest station number thermocouple or
convection type gauge controls the on-off operation of the cold cathode gauge.
4. A cold cathode gauge can ignore this control feature by selecting "None" on the PC jumper.
If MPI is selected, the cold cathode gauge will be shut down when the pressure at the lowest station numbered
thermocouple or convection type gauge reaches a particular pressure. In this case, the cold cathode gauge should
be assigned to an "odd" station number. The display will then show "OFF" when it is in shut-down.
Likewise, if MPI#2 is selected, the cold cathode gauge should be assigned an "even" station number.
The pressure at which shut down occurs, when using MPI or MPI#2, depends on the configuration of the MM200.
If any 7Es or a 3D or 3E is installed, the pressure will be twenty microns, otherwise, it will be 10 microns.