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9.1 Isolate the cause
9.1.1 When a measurement problem occurs, the first step is to try to isolate the cause. If
the DOCN600 is powered, go through the menu and check your settings. A
convenient way to do this is to call TEST. See Section 5.5.
9.1.2 If your DOCN600 appears dead or intermittent, check the breaker, make sure that
the instrument is set up for the available line voltage and make sure the line voltage
is actually available at the terminals. Now measure that sufficient voltage is
available at all times; it should be 98 Vac to 132 Vac or 187 Vac to 243 Vac
respectively. Shut line power off, making sure it is off. CAUTION: Power to the
relays may be supplied from a separate source, shut it off too. Check and if
necessary replace the internal 0.25A fuse. Push the connector of the ribbon cable
firmly into its socket. If these steps do not solve the problem it may be necessary to
replace the power supply board. See Section 9.3.1 below.
9.1.3 If the process value seems wrong, clean the sensor as described in Section 6.1.3.
Inspect the sensor, wire, terminal block connections and interconnections.
Calibrate and resume operation.
9.1.4 To find out whether the problem is in the sensor, or in the analyzer, use the self-
testing features. Leave the instrument in RUN mode and proceed as follows:
a) Move the slide switches S40 and S41 on the back of the swing-out panel from
position "ON LINE" to position "TEST."
b) Press CALL to enter the menu and go to “%sat/ppm.”
c) Set the D.O. simulation DIP switch Bank S42 switch No. 1, On, Switches No. 2,
3, and 4, Off. The display should show 4 ppm ±5%.
d) Now proceed to turn each of the other S42 switches On with the remaining
switches Off.
The display should read within 5% of 10 ppm with switch 2 On, 16 ppm with
switch 3 On, and 20 ppm with switch 4 On.
If this is the case the analyzer is in order and the problem is with the probe.
e) Return S40 and S41 to “On line” and ensure that all S42 switches are Off.
9.1.5 a) To check the temperature channel move the slide switches S40 and S41 from
position “On line” to position “TEST”.
f) Set the DIP switch 1 Bank S1 On.
g) Go to the TEMPERATURE menu item.
d) Set the temperature simulation DIP switch Bank S43 switch No. 1 On, switches
No. 2 and 3 Off. The display should show 10 degrees Celsius ±5%.
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