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Normal temperature range

Most standard transducers will operate from 0∞F to 180∞F.

High temperature measurements

Special transducers and couplants are available for temperatures above 180∞F up to

650∞F with intermittent contact. It is necessary to cool the transducer, by submerging

the transducer in water between readings, when measuring high temperatures.

Modes and temperature errors

In addition to errors caused by velocity changing with temperature, some modes (meas-

urement techniques) are affected more than others. For example, dual element mode has

larger errors due to changes in temperature of the delay line. However, in multi-echo

techniques, auto temperature helps to minimize these errors.

4.6 Measurement Modes

In this section we will discuss the different measurements modes the TI-CMX is capable

of operating in, the transducers required, and the reasons for using specific modes:

Pulse-Echo Mode (Flaw & Pit detection) – Coating Off (P-E)

Pulse-echo mode measures from the initial pulse (sometimes referred to as an artificial

zero) to the first echo (reflection). In this mode, either an automatic or manual zero can

be performed depending on the zero probe function setting. If the manual mode has been

selected, the transducer is placed on a reference disk, located on top of the TI-CMX, and

a key is pressed to establish a zero point for the particular transducer. If the Auto Zero

feature is enabled, a simple key press will perform an electronic zero to establish the

same zero point.

In this mode errors result from surface coatings and temperature variations.

Since pulse-echo only requires one reflection, it is the most sensitive mode for measur-

ing weak reflections (flaws) typically found when measuring heavily corroded metals.

V-Path Correction

Dual element delay line transducers have two piezoelectric elements

mounted at an angle on one end of the delay line. One element is

used for transmitting sound, while the other element only receives

sound. The two elements and their delay lines are packaged in a sin-

gle housing but acoustically isolated from each other with a sound

barrier. This allows the transducer the ability to achieve very high

sensitivity for detecting small defects. Also, the surface of the test

material does not have to be as flat in order to obtain good measure-

ments.

Dual element transducers are normally used in pulse-echo mode for

finding defects, and in echo-echo mode for through coating measurements.

Dual element delay line transducers are usable over a range of 0.025 inches to 20 inches

depending on the material, frequency, and diameter.

A limitation of dual element delay-line transducers is the V shaped sound path. Because

the sound travels from one element to another, the time versus thickness relationship is

non-linear. Therefore, a correction table in the instruments software is used to compen-

sate for this error.

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Dual Element

Transducer

showing

V-path of signal

9.3 Coating Calibration (PECT)

Known Velocity

If the coating velocity is known, the user may wish to simply enter the velocity number

into the TI-CMX, rather than have the TI-CMX calculate the velocity value using a

known thickness on a coating sample(s). The steps for entering the velocity are outlined

below:

Using a Known Material Velocity

1. Press the MENU key once to activate the menu items tab.

Press the MENU key multiple times to tab right and the ESC

key multiple times to tab left until the CAL menu is

highlighted and displaying the submenu items.

2. Use the UP and DOWN arrow keys to scroll through the sub

menu items until COATING VEL is highlighted.

3. Press the ENTER key to display the Digits Edit Box.

4. Press the UP and DOWN arrow keys to scroll the highlighted

value.

5. Press the LEFT and RIGHT arrow keys to scroll the digit

locations.

6. Repeat steps 4 & 5 until the velocity number is correctly

displayed.

7. Press the OK key to set the velocity and return to the menu

screen, or ESC to cancel entering the velocity.

8. Finally, press the MEAS key to return to the measurement screen and begin taking

readings.

Known Thickness

Sometimes the sound velocity of a coating material is unknown. In this case a sample

with a known thickness can be used to determine the sound velocity of the coating. As

previously discussed, the TI-CMX offers a one point calibration option for coating in

PECT measurement mode. It is also import to reiterate that the coating sample must be

coupled to a metallic material in order to perform the calibration. The calibration should

also consider calibrating on high side of the intended measurement range, when using

the one point option, minimize overall error. For example, if the measurement range of

the coating will be from .040” - .080” (1.0mm 2.3mm), a coating closest to .080

(2.0mm) should be used.

NOTE: It’s always handy to carry a set of mechanical calipers to

use in conjunction with the TI-CMX for calibration in the field:

One Point Calibration

NOTE: Be sure that the probe zero procedure has been performed

prior to performing this calibration procedure.

1. Physically measure an exact sample of the coating using a set

of calipers or a digital micrometer.

NOTE: The coating sample must be coupled to a metallic material

in order to be calibrated.

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