PZX-7
Ultrasonic Multi-Mode Thickness Gauge
11
3.5 Temperature
Temperature has an effect on sound velocity. The higher the temperature, the slower
sound travels in a material. High temperatures can also damage transducers and
present a problem for various liquid couplants.
Since the sound velocity varies with temperature it is important to calibrate at the
same temperature as the material being measured.
Normal temperature range
Most standard transducers will operate from 0
F to 250
F.
High temperature measurements
Special transducers and couplants are available for temperatures above 250
F up to
1000
F with intermittent contact. It is necessary to cool the transducer by
submerging it in water between measurements.
Modes and temperature errors
In addition to errors caused by velocity changing with temperature, some modes
(measurement techniques) are affected more than others. Multi-echo techniques
offer temperature compensation to help minimize these errors.
3.6
Measurement Modes
This section will cover the different measurements modes of the
PZX-7
, the
transducers required, and the reasons for using specific modes:
Pulse-Echo (P-E) Mode:
Pulse-echo mode measures from the initial pulse (sometimes referred to as an
artificial zero) to the first echo (reflection). In this mode, a manual zero using the disk
(battery cover) will need to be performed prior to calibrating the
PZX-7
. The
transducer is placed on the reference disk located on top of the
PZX-7
, and the
PRB
0
key pressed to establish a zero point for the transducer connected.
Errors from surface coatings and temperature variations can occur in pulse-echo
mode. Therefore, coatings should be removed, and frequent probe zero’s should be
performed if experiencing temperature gradients.
Echo-Echo (E-E) Mode – Through paint
The echo-echo mode measures between the first and second return
echoes/reflections. This mode is most commonly used with the high frequency delay
line style transducers for thin materials, and will also eliminate compensate for
temperature. This technique will also eliminate error due to epoxy based coated
surfaces by eliminating the error from the coating and measuring only the second
layer or base material without having to remove the coating. The disadvantage is
Summary of Contents for PZX-7
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