MTI AccuMeasure 9000, User Manual

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Panel – Bargraph Display, Figure 5: Accumeasure™ 9000-2 Front Panel-Digital Display, and Figure 4:
Accumeasure™ 9000-2 Front Panel-Bargraph Display. The
offset switch indicator is a blue, LED lamp
that is lighted when the offset switch is positioned in its “in” position and the front panel located, external
offset potentiometer, is engaged.
The Accumeasure 9000 probe amplifier has a bargraph display on the front panel to indicate the value of
the probe-to-target gap. Each bargraph is a ten element, green LED array that is calibrated to display,
/-5% of the full scale probe range, the relative gap value. The number of display elements lighted
indicates the gap magnitude. For instance, for a gap value between touch and 10% of the full-scale gap,
only the left element is lighted, and for a gap value between 50% and 60% of full scale, the six left
elements are lighted. The location of the
bargraph display (s) is shown on Figure 2: Accumeasure™
9000-1 Front Panel – Bargraph Display and Figure 4: Accumeasure™ 9000-2 Front Panel-Bargraph
Display.
A back lighted, digital panel meter to display the probe gap signal for each probe channel is available, as
an option, to replace the bargraph display in the Accumeasure 9000. The meter has a 3 1/2 digit display
that is calibrated to produce a reading equal to the rear panel output signal voltage with a full scale range
of +/-10.00 VDC. The meter has a resolution of 0.01 VDC, and an accuracy of +/-0.02 VDC. The location
of the
digital display (s) is shown on Figure 3: Accumeasure™ 9000-1 Front Panel – Digital DisplayFigure
5: Accumeasure™ 9000-2 Front Panel-Digital Display.
3.5 Probe Mounting
Since Accumeasure
TM
9000 measures probe-to-target gap, the probe fixture must have good mechanical
stability and alignment. The fixture must hold the probe securely and maintain the probe face parallel to
the target surface. Probe tilt causes measurement errors, so a tilt of less than 5% of range is
recommended. That would mean that for a 500um (20 mil) range sensor, the edge of the sensor should
tilt no more than 25um (1 mil) on a side.
It is recommended that the probe fixture be connected to the same ground return as the target if the target
is grounded. The fixture should have a noise-free, low-impedance return path to the DC supply ground of
the power supply that provides the DC voltages to the Accumeasure
TM
9000 single channel probe
amplifier board unit. Values of up to 1 kilo-ohm resistance may be tolerated under certain conditions, such
as when maximum system linearity and resolution are not required.
If a direct ground connection is not possible, a capacitive-coupled connection can be used. Be aware that
a 350pF value in the return path will introduce a small amount of measurement noise. Larger
capacitances will introduce correspondingly smaller amounts of noise (1000pF or larger is recommended).
In practice, the ground return path may be provided automatically if the target is at ground potential and is
connected back to the amplifier ground connector through the ground terminal on the AC supply line. To
minimize the measurement noise, connect a ground lead directly from the probe fixture and target to the
ground connector on the probe amplifier module.
The probe should be mounted to meet two important conditions:
1) At a minimum excursion, the probe-to-target gap should be no less than 5% of the probe range.
2) At maximum excursion, the target gap must not exceed 95% of the full-scale probe range.
Before performing a measurement, ensure that the probe and target under test are clean and free from
debris.
CAUTION
The probe connector and the probe body on ASP-1, ASP-2, ASP-5, and ASP-10 probes carry a 3 to
5Vrms electrical guard voltage for the cable shield and the probe. These must not be shorted to ground
by the fixture or the system will be inoperative.