15
CHAPTER FIVE
MAKING MEASUREMENTS
The steps involved in making measurements are detailed in this section. The
following sections outline how to setup and prepare your
PZX-7
for field use.
In pulse-echo mode the probe zero must be performed on the reference disk (battery
disk) attached to the top of the instrument. This compensates for variation in the
transducer. In all modes the sound velocity must be determined. The sound velocity
is used to convert the transit time to a physical length. The sound velocity can be
selected from the material chart at the end of this manual, or for greater precision
determined by measuring and calibrating from a known thickness of the actual
material. To enter the velocity from a table, look up the material on the chart in the
appendix of this manual and refer to the section below on Calibration to a Known
Velocity. To determine the velocity of a single sample, refer to the Material
Calibration section on page 16.
When measuring curved materials, it’s more accurate to calibrate from two test
points, one at the minimum limit of the target thickness and one at the maximum limit.
In this case the reference disk is not used, and considered a ‘two-point’ calibration
described on page 19.
5.1 Probe zero
A probe zero is only necessary if a contact style transducer is used in pulse-echo
mode, and the contact option is enabled in the menu. A probe zero should be done
prior to calibrating the instrument, and done on a periodic basis when a temperature
gradient is an issue. If the
PZX-7
is not zeroed correctly, all measurements will be in
error by some fixed value. In order to perform a probe zero, you must be in pulse-
echo mode.
Setting the zero point of the
PZX-7
is important for the same reason that setting the
zero on a mechanical micrometer is important. It must be done prior to calibration,
and should be done throughout the day to account for any temperature changes in
the probe. If the
PZX-7
is not zeroed correctly, all the measurements taken may be
in error by some fixed value. The zero can only be performed with the measurement
mode set to pulse-echo (P-E). Therefore, if the
PZX-7
is to use the echo-echo (E-E)
measurement mode and a manual zero is being performed, the
PZX-7
will argue by
briefly displaying the message “ERR”.
The procedure to zero the transducer is outlined as below:
Performing a Manual Probe Zero (On Block)
Summary of Contents for PZX-7
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