Delay Line Tips for Precision Ultrasonic Transducers

What delay line tips are

A delay line tip is a tip made of a plastic material (acrylic or graphite) that screws or clips onto the single element probe. It works as an acoustic delay line: the ultrasonic signal travels first through the material of the delay line and only then enters the part to be measured.

This “delay” shifts the surface echo of the part in time, separating it from the initial echo generated by the crystal. The result is that the measurement time window becomes clean even on very thin materials, where the two echoes would otherwise overlap and prevent the reading.

The two Dakota materials: acrylic and graphite

Acrylic (codes F-000-71xx, X-132, X-152, X-532, X-752)

Acrylic delay line tips (PMMA or equivalent) are suited to thickness measurement on:

• Steels: carbon, stainless, alloyed
• Aluminium and light alloys
• Titanium and aerospace alloys
• Rigid materials with a medium-high velocity of sound

They are to be used with the gauge set to Interface-Echo mode (echo from the entry surface of the material) or to Echo-Echo mode (multiple echo, for high-precision differential measurements).

Graphite (codes X-533-0000 and X-633-0000)

Graphite delay line tips are suited to thickness measurement on:

• Thin plastics, film, packaging
• Technical rubbers, gaskets, O-rings
• Polymer-based composite materials
• Materials of low acoustic impedance and a velocity of sound below 2000 m/s

They are to be used with the gauge set to Plastic Mode, which applies correction factors specific to polymer materials.

Representative models from the catalogue

A selection of representative models from the 13 Dakota delay line tip codes available for prompt delivery.

Compatible Dakota thickness gauges

• PCX8-DL — supports acrylic (interface-echo) and graphite (plastic mode)
• PMX2-DL / PMX3-DL — support both modes
• PMX4-DL — optimised for delay tips with frequencies of 500 kHz – 10 MHz
• PZX1-DL — basic interface-echo support with an acrylic delay tip

How to choose the delay line tip

• Thin steel or aluminium: acrylic F-XXX in interface-echo mode
• Plastic or rubber: graphite X-633-0000 in plastic mode
• Measurement of the highest precision: acrylic in echo-echo mode (it subtracts the surface echo)
• Probe frequency 5 MHz: F-000-7102 / F-000-7103
• Probe frequency 10 MHz and above: F-000-7104 / F-000-7105 / F-000-7106
• Thin plastic: X-132-0000 or X-152-0000

Maintenance and service life

Delay line tips are components subject to wear: repeated contact with the surface of the material produces scratches and abrasion which, beyond a certain point, alter the velocity of sound in the delay line and introduce measurement errors. It is recommended to:

• Check periodically that the tip is flat, using a calibration block
• Replace the delay tip if there are deep scratches or uneven wear
• Store it in a dedicated case, avoiding contact with abrasive dust
• Always use couplant, at the delay tip – material interface as well
• Keep in stock at least one spare delay tip for each working configuration

Typical applications

• Food packaging: thickness measurement of cans, trays, film
• Pharmaceutical sector: blisters, containers, quality control
• Aerospace: thin laminates, skin sheets
• Industrial plastics: corrugated pipes, profiles, films
• Electronic components: displays, sensors, micro-parts

Complementary accessories

Delay lines are paired with precision single element probes. For correct calibration, calibration blocks of known thickness are useful.

Field of application by industrial sector

Dakota interchangeable delay line tips are key components for precision measurement in every sector that requires sub-millimetre accuracy on thin materials.

• Food packaging: thickness measurement of cans, trays and plastic packaging film. Graphite delay tips in plastic mode reach the 0.127 mm accuracy required by many process specifications.
• Pharmaceutical sector: blisters, drug containers, technical labels. Thickness measurement documents the conformity of the moulding and extrusion process.
• Aerospace: thin laminates in composite materials, metal sheets for structural panels. Acrylic delay tips with the PCX8-DL gauge cover the sector’s typical specifications.
• Precision automotive: high-strength pressed sheet for bodies, thin profiles for engine gaskets. Delay lines bring the lower measurement limit below a millimetre.
• Industrial plastics: corrugated pipes, extruded profiles, technical films. Graphite delay tips are the instrument of choice for quality control in production.
• Electronic components: LCD displays, OLED panels, MEMS sensors. Frequencies of 15-25 MHz reach the resolution required by the advanced electronics industry.

Why choose original Dakota accessories

Dakota delay line tips are machined to optical tolerance on the contact surface, an essential requirement for precision measurements on sub-millimetre thicknesses.

• Guaranteed compatibility with every instrument in the Dakota line
• Immediate availability from the RODER SRL warehouses in Italy, the United Kingdom and the United States
• Traceability of the batch and dedicated after-sales support
• Certificates and datasheets in compliance with the requirements of Directive 2014/68/EU PED where applicable
• Technical support dedicated to choosing the right component

Frequently asked questions

When must I replace a delay line tip?

A delay line tip should be replaced when it shows deep scratches or uneven abrasion, or when a check on a calibration block shows a drift in the velocity of sound of more than 2%. It is recommended to keep at least one spare tip in stock for each working configuration.

Can I use an acrylic delay tip on plastic?

Technically possible, but not optimal: the acoustic impedance of acrylic is closer to metals than to plastics. For measurements on plastic the gauge should be set to Plastic Mode with a graphite delay tip, which has a lower acoustic impedance and improves signal transfer.

Do all single element probes accept interchangeable delay tips?

No: only probes with the standard Dakota thread accept screw-on delay tips. “Monolithic” contact precision probes cannot be modified with a delay tip. Always check compatibility in the probe datasheet.

Does the delay line introduce measurement errors?

A new, correctly calibrated delay line tip does not introduce significant errors: the gauge automatically compensates for the time of flight in the delay line. The error grows with wear: this is why it is important to check periodically with calibration blocks.

What is the minimum measurable thickness?

With an acrylic delay line on steel: typically 0.15 mm at 10 MHz, down to 0.08 mm at 25 MHz. With a graphite delay line on plastic: typically 0.127 mm. The exact specifications depend on the probe-tip-instrument combination and should be verified with a preliminary calibration.

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Request availability and a quotation: contact us stating the model of your single element probe and the intended application.