3.2. Analog Output (4-20mA)
The HPM-2002-OBE with analog output and display is shown in the figure below. The user interface consists of a status bar, a mode bar, and setpoint test jacks.
3.2.1.Overall Functional Description
The status bar gives information about the condition of the HPM-2002-OBE. High and Low indicate whether the set points are activated. Error indicates if there was a problem downloading the EEPROM. Torr and mTorr indicate what pressure regime the gauge is measuring.
The mode bar indicates which mode has been selected. The HPM-2002-OBE has five modes which the user may enter. This is similar to the six modes which can be entered in the bench top/panel mounted HPM- 2002, there is no interlock feature; when the user changes the settings within a mode any adjustments that have been made will be permanent once the mode is exited. (To exit without making changes permanent, the user must turn the power off.)
3.2.2.High and Low Set Point Modes
The HPM-2002-OBE provides TTL outputs for process control. These signals are available on the 15-pin connector (see previous table in Section 2.4).
To view the High set point, place the HPM-2002-OBE in the High mode by pressing the SELECT button until the High mode light is illuminated. The display then shows the set point selected. During normal operation the alarm light will illuminate and the TTL output (pin # 1) will go high (+5V) if the pressure exceeds the set point.
Similarly, to view the Low set point, place the HPM-2002-OBE in the Low mode by pressing the SELECT button until the Low mode light is illuminated. The display then shows the set point selected. During normal operation the alarm light will illuminate and the TTL output (pin # 2) will go high (+5V) if the pressure becomes less than the set point.
To adjust a setpoint, place the HPM-2002-OBE in either setpoint mode (High or Low). Next, use the ADJUST rotary encoder until the desired setpoint is displayed. Finally, place the HPM-2002-OBE back in the Run mode. The new set points are now stored in the HPM-2002-OBE’s memory.
3.2.3.Run Mode
The HPM-2002-OBE will automatically enter the Run mode upon start-up. This is the mode for normal operation and the mode in which the instrument will spend most of its time. In the Run mode the HPM-2002-
