To perform a full calibration on the HPM-2002-OBE, first use the Zero Coefficient Adjustment Procedure. Followed by the Midrange Coefficient Adjustment Procedure, and finally perform the Atmosphere Coefficient Adjustment Procedure. Sensor Coefficients are stored in the Sensor’s EEPROM upon exiting the Cal mode.
3.2.5.GAS Mode
The HPM-2002-OBE can provide true pressure measurements in many gas environments. At pressure levels where the direct force piezoresistive sensor is operative, the instrument is gas composition independent and measures the true pressure regardless of gas composition. The Pirani is gas composition sensitive so the actual composition must be known and the Pirani calibrated in that gas. When the vacuum system’s gas composition is dominated by a single gas species (for example, during system venting with an inert gas), the user can enter a gas selection into the HPM-2002-OBE by rotating the ADJUST rotary encoder. To view the gas selection, depress the SELECT button until the GAS light is illuminated. The number on the display corresponds to the gas. See the table below.
Gas Selection Table
Gas Mode | Gas |
Displayed Number | |
| |
00 | Nitrogen |
| |
01 | Argon |
| |
02 | Helium |
| |
03 | Water Vapor |
| |
04 | Custom |
| |
3.2.6.Analog Output (4-20mA)
The dual output option board provides current output proportional to the HPM-2002-OBE’s pressure reading. The first channel (pins 5 & 10) corresponds to the higher-pressure range (1-1024 Torr). The second channel (pins 7 & 11) corresponds to the lower pressure range (0-1000 mTorr). The equation below gives the output current of the pressure:
| | | | | |
Ι(channel1) = 4mA + (p(Torr))* | | 16mA |
1024Torr | | |
| ⎛ | 16mA ⎞ |
Ι(channel2) = 4mA + | (p(mTorr ))* ⎜ | | | ⎟ |
| |
| ⎝ | 1000mTorr ⎠ |
Note that for both channels, the output is always between 4mA and 20mA specifically, when the pressure goes below 1 Torr, channel 1 current will be approaching its minimum of 4mA and when the pressure is above 1 Torr, channel 2 current will be 20mA.
HPM-2002-OBEVacuum Gauge | Page 15 of 39 |
