COSA Xentaur Xentaur XDT - Manual (Page 35)

XDT User’s Manual
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respectively. Pressing the “MODE” button will move the cursor (flashing digit) to the right. Press-
ing and holding the “MODE” button will signal the instrument to read the password and if correct
to unlock the instrument. As discussed above an unlocked instrument will display “
SET UN/LOC”.
The user may enter the assigned password by pressing the UP, DOWN and MODE buttons. The
first digit is unique in that it consists of 1½ digits in the range of -19 to 19, this allows entering the
full range of assignable numbers.
An example is used to illustrate the unlocking of a password-protected instrument. Suppose the
password is 1234. After an attempt to unlock, the user will see “SEC” followed by “000”, with the
first 0 flashing. Pressing the “UP” button twelve times will display “1200” (overshooting a num-
ber can be corrected by reversing the use of the UP and DOWN keys), with the “12” flashing.
Pressing the “MODE” button will flash the next “0”. Pressing the “UP” button three times will
display “1230”. Pressing the “MODE” button will flash the last “0”. Pressing the “UP” button
four times will display “1234”. Pressing and holding the “MODE” button, will display “
SET UN/
LOC”, indicating that the instrument is now unlocked. It may be locked without the password,
same as any other instrument.
Note: To avoid unauthorized changes, it is imperative that instrument is returned into the locked
mode.
11. Sensor Cable Compensation: As noted in other paragraphs this instrument measures the
impedance of the sensor (in the form of attenuation in decibels) from which it computes the
dewpoint. At very low dewpoints the sensor capacitance is small enough to be in the same
order of magnitude as a long coaxial cable. Thus the measurement circuit must be compen-
sated for the impedance of the sensor cable. Instruments which are delivered with a cable
are already compensated at the factory and should not be compensated again, however if
a new cable is connected, the following procedure should be used for compensation (also refer
to the Set-Up State flow diagram in Appendix A):
a. Disconnect the sensor from the cable by unplugging the BNC connector, keep the cable
connected to the instrument.
b. Prepare a means by which the BNC connector at the end of the cable could be reliably
shorted (using a jumper clip etc.), do not attempt to short at the instrument screw terminals as
this approach will not account for the cable resistance.
c. Go to the CNF/CBL/OPN (Confirm Cable Open) mode.
d. Leave the BNC connector open and press the UP key. The instrument will show OPN and
beep for a few seconds. Then it will show CNF/CBL/SHR (Confirm Cable Short).
e. Short the BNC connector and press the UP key, the unit will show SHR and beep for a few
seconds. Then it will show CNF/CBL/OPN again.
f. Leave the BNC connector open again and press the UP button. The instrument will show
OPN and beep for a few seconds. Then it will show END
The compensation data will be retained even if power is turned off.
3.5 Resetable Audio-Visual Alarm Option (NFPA compliant)
When the instrument is ordered with an Audio-Visual Alarm option, it is provided in the XDT-
NEMA enclosure, outfitted with two front panel momentary push buttons in NEMA sealed rubber
boots. The instrument complies with the recommendations of NFPA 99, 1996 edition.