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The DR-7 displays the time (in seconds) that each sample takes to complete. The sample time is defined
as the time required from when the DR-7 detects the oil at its DL and DS sensors, to the time the last of
the oil passes the end of oil sensor. The timer is located under the DL and DS blocks just above the
STANDARD button indicated as 000.
Knowing the time each sample takes to complete can be used to catch a bad sample test. For example, if
previous samples required an average of 200 seconds to complete and the next sample, of the same oil,
requires only 100 seconds, the sample test is in error and must be repeated. Sample times will vary
somewhat, however, significant differences in time are usually caused by false tripping of the end of oil
sensor by a large particle in the sample. This requires adjustment to the end of oil sensor’s threshold or
bypassing the End of Oil Sensor by leaving the capillary tube outside of the sensor during the test. See the
END OF OIL SENSOR CALIBRATION in section 8. Calibration of this manual. The time will retain the
last sample time until the next sample is started.
If, for some reason, a sample is running through the precipitator tube for 12 minutes, the DR-7 will end
the test and freeze the readings at this time. “TIMED OUT” will appear next to the timer below the DL
and DS boxes. This might be caused by the sample being too viscous. The sample should be thinned with
more heptane or diluent oil and run again for accurate results.
7.1.1 – STANDARD Operation
The black shrink tubing should be placed against the left edge of this assembly to run the test to ensure no
light intrusion. A depress lever is located to the left of the optics assembly to open and hold the
precipitator gate in the up position to allow for the precipitator insertion under the optics. Moving the
lever forward opens the gate while moving the lever back will close the gate. When closing the gate, the
lever should be pushed back until its stops which will clamp and hole the precipitator tube.
1.
Mix the oil sample as described in section 6.1
Preparing an Oil Sample for Testing
of this manual.
Put the sample in the vial tube holder at the top of the instrument.
2.
Install a precipitator tube by first moving the depress lever forward on the left-hand side of the optics
assembly to open and hold the precipitator gate in the up position. Insert the glass part of the
precipitator tube under the optics block and then move the lever backwards while pressing down on
the gate until its stops to hold the precipitator tube in place. The black shrink tubing of the precipitator
tube should be tight against the left-hand side of the Optics Block. Next, place the short end of tygon
tubing onto the barb fitting on the left bulkhead barb under the display screen.
3.
Weave the capillary tube between the tubing guide pins as shown below. Weaving the tube through
the pins will help keep the precipitator tube from sliding out of position. Then place the capillary tube
in the center groove of the end of oil sensor and close the door by snapping it shut. Be careful not to
pinch the tubing with the door.
