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HPM-2002-OBEVacuum Gauge Page 35 of 39
communications program (e.g. WindowsÔ Hyperterminal) which can be used to communicate with RS232
versions of the HPM-2002-OBE. The Transmit Device Status (“S<CR>”) command will retrieve the
HPM-2002-OBE’s status register. A successful read of the status register will clear the “Err4” condition.
What are Err3, Err5, Err6 and Err7?
These are simultaneous error conditions, i.e. Err3 = Err1+Err2.
Why does my display read, “U.U”?
“U.U” stands for unconnected piezo/unconnected Pirani. This message indicates that the voltage readings
from the sensors are outside any usable range. Most often this occurs when there is no sensor tube connected
to the HPM-2002-OBE. This error will also occur if there is a problem with the user’s DC power supply.
Verify that the voltage supplied to the HPM-2002-OBE is within the specified range using a voltmeter at
pins 3 and 4 on the power cable. After power verification and with the voltage still applied, hot plug the cable
into the HPM-2002-OBE. If the “U.U” still appears, most likely the sensor tube (HPM-2002s) needs to be
replaced.
Why does my display read, “U .”?
“U.” stands for unconnected piezo. This message indicates that the voltage reading from the piezoresistive
sensor is outside any usable range. While this message can mean that the sensor tube (HPM-2002s) will
need to be replaced, it can also indicate that the piezo zero calibration parameter, which is stored in the
sensor tube’s EEPROM, has become corrupted or lost. (See next FAQ)
Why does my display temporarily show, “U .” as I pump the system down?
“U .” stands for unconnected piezo. This message may flash near the dual sensor crossover pressure range if
the piezo zero calibration parameter has been corrupted or lost.
The RESTORE CALIBRATION command will download the calibration parameters from the HPM-2002-
OBE to the sensor tube. See the advanced setup guide (Section 5.1) for more information. If the error
persists at the crossover point, then a calibration of the Piezo sensor should be performed. The Piezo Zero is
updated when the Pirani pressure is less than 125 mTorr. In order to update and save the Piezo Zero
parameter:
• Pump out to 100 mTorr or less
• Using SELECT, step to the CAL function
• Rotate ADJUST one step in either direction and then back to its original position (CAL light starts
flashing)
• Using SELECT, exit the CAL function and return to the Run mode
Changing the Piezo Zero will shift the atmospheric reading by the same amount. therefor the atmospheric
readong should also be checked and re-adjusted if necessary.
Why does my display read, “. U”?
This message indicates that the voltage readings from the thin film Pirani sensor are outside any usable
range. This usually indicates that the sensor is defective and will need to be replaced.