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 64 of 160
TELEVAC
When this pushbutton is pressed in normal operation, the sensitivity of any thermocouple sensor displayed in the
right hand display is adjusted to correspond to operation in a gas other than Nitrogen (or air). Typically the gas is
argon and the default programming is for argon. The GAS display LED is illuminated. The alternate gas sensitivity
stays with that station even if it is moved to the left hand display. Pressing this button a second time, when the
desired station is displayed in the right hand display, causes the gas LED to go out, and the sensitivities to return to
normal (i.e., air or nitrogen). Some or all of the thermocouple stations can be changed in this way one at a time.
The N2/GAS pushbutton is disabled when the LOCK/SETUP switch is in the LOCK position. It can be overridden
by an external GAS switch, which can be connected via a connector marked "GAS SW" on the RS232 module. The
connector is a NC connection until a mating plug is inserted. The external switch should be wired so that it is
CLOSED for N2 and OPEN for the alternate gas.
LEAK RATE PUSHBUTTON
When the leak rate pushbutton is pressed in normal operation, the MICRONS per HOUR display is illuminated.
The right-hand display starts to indicate leak rate in microns per hour based upon the sensor associated with
station #1, even if this display had been previously indicating another sensor or in some other units. The display is
continuously updated based upon the change in pressure from the time when the button was first pushed. Initial
readings are displayed after a 15-second delay. Typically a 15-minute waiting time is used to get a final reading.
Pressing this button a second time returns the instrument to the set-up that was in effect before the button was
pressed the first time. This feature applies to thermocouple and convection gauges only.
HANDLING UNITS
Sensor signals are processed and linearized in "native" units of pressure; that is, the units, which are normally
considered standard for the unit being processed:
Thermocouple - microns
Convection
- microns or Torr (per Table 4.1)
Cap Dia
- microns or Torr
Ion (CC)
- Torr
Analog recorder outputs are in "native" units of pressure. Selection of alternate units on the display does not affect
the recorder outputs. If this is not done, recorder charts read incorrectly when someone changes units with the
front panel pushbutton.
Customers who desire recorder outputs to correspond to different units of measurement should contact Televac.
When the setpoint function is advanced to one of the setpoints "on" or "OFF" selection modes, the stored setpoint
setting is converted to the selected unit, if different from the native unit. This then is the setpoint setting that is
displayed. Changing this setting with the UP/DOWN arrows only affects the display. Upon leaving that function,
the displayed value is converted to binary, then to the native unit for the sensor that corresponds, and is stored as
such. At that moment the new value becomes the effective value for that setpoint. While adjusting "on" or "OFF"
setpoints, it is not possible to change "UNITS".
When a unit other than the native unit is selected for display, a conversion will be made from the native unit to the
selected unit before the display value is sent to the display buffer.