Transducers for Precision Thickness Gauges

The three families of single element transducer

Single element transducers have one piezoelectric crystal that transmits and receives alternately. Compared with dual element probes they offer higher spatial resolution and higher frequencies, but they require relatively smooth surfaces and materials that attenuate little. They are the right choice when dual element probes cannot resolve sub-millimetre thicknesses, or when the precision required is better than 0.01 mm.

Single Element Contact (direct contact)

Contact precision probes are designed for direct contact with the surface of the material. They are the largest family: they include frequencies from 2.25 MHz up to 25 MHz, with compact diameters from 1/4″ to 3/4″. The T-402, T-403, T-404 and T-857 configurations cover every typical need of quality control in production and of precision inspection.

Delay Line and Pencil Transducers

Delay line probes incorporate a delay line (of acrylic or graphite) between the crystal and the contact surface. This line moves the surface echo away in time, making it possible to distinguish the back-wall signal even on very small thicknesses (from 0.127 mm on plastic with dedicated probes). They are indispensable for measuring:

• Plastic films, food packaging, pharmaceutical blisters
• Thin foils of aluminium, copper, brass and packaging alloys
• Technical glass for optoelectronic components
• Aerospace components with very tight tolerances
• Coating layers on metal

Pencil probes with delay tip

Pencil probes are pencil-shaped single element transducers with an interchangeable tip (delay tip). They are meant for restricted access such as holes, grooves and slots, where standard probes cannot sit flat. The delay tips are available in acrylic (for steel, aluminium and titanium) and graphite (for thin plastics) versions and can be replaced without changing the whole probe.

Frequencies and typical applications

• 2.25-5 MHz: general measurements on steels and metallic materials of medium thickness
• 10 MHz: standard precision on thin metals, glass and homogeneous alloys
• 15 MHz: high resolution for packaging, film and sub-millimetre decorative foils
• 20-25 MHz: the highest resolution available, for aerospace, electronics and research applications

Representative models from the catalogue

A selection of representative models from the 99 Dakota single element codes available. For the complete list, contact our technical office.

Compatible Dakota precision thickness gauges

• PCX8-DL — precision thickness gauge with data logger and graphic display
• PMX2-DL / PMX3-DL — basic precision thickness gauges with data logger
• PMX4-DL — high penetration, optimised for 500 kHz – 10 MHz probes
• PZX1-DL — entry-level precision thickness gauge
• BT1-DL / BT2-DL — bolt tension monitors (with dedicated probes)
• CMX10-DL — in single element mode

How to choose the precision transducer

• Small thicknesses (sub-mm): delay line probes at 10-25 MHz
• Plastic materials and packaging: graphite delay tip with Plastic Mode
• Thin steels and metal foils: 10-15 MHz contact precision
• Glass and ceramic materials: 5-10 MHz contact
• Restricted access: pencil probe with interchangeable delay tip
• Bolt tension: dedicated probes for the elastic elongation of fasteners

Typical applications

• Quality control in the production of tubes, sheet and thin profiles
• Packaging measurement in food, pharmaceuticals and cosmetics
• Aerospace and automotive components of high precision
• Technical glass for optics, displays and optoelectronic components
• Laminated foils, cans and metal containers
• Measurement of coatings and sub-millimetre dielectric layers

Complementary accessories

For precision measurements the couplant and the calibration blocks are an integral part of the system. Interchangeable delay line tips and probe cables with Microdot and LEMO 00 connectors complete the range.

Field of application by industrial sector

Dakota precision single element transducers cover every industrial sector that requires non-destructive thickness measurement of high accuracy. The most frequent application contexts are given below.

• Aerospace: thickness measurement of thermal coatings, thin composite laminates and skin sheets of structural panels. Probes of 15-25 MHz with an acrylic delay line are the standard for the sector’s typical specifications.
• Precision automotive: quality control of pressed sheet for bodies, thin profiles for gaskets and electromechanical components. Probes of 10 MHz with the PMX2-DL gauge cover most requirements.
• Food and pharmaceutical packaging: thickness measurement of blisters, trays, cans and caps. Graphite delay line probes in plastic mode guarantee accuracy better than a tenth of a millimetre.
• Glass sector: thickness measurement of technical glass for optics, displays and photovoltaic panels. Contact precision probes of 5-10 MHz with a couplant made for glass work effectively on optically transparent materials.
• Electronic components: measurement of dielectric coatings, LCD displays and MEMS sensors. Very high frequency probes (20-25 MHz) reach the resolution these applications require.

Why choose original Dakota accessories

Every Dakota single element transducer is an original component, guaranteed for mechanical and electrical compatibility with Dakota precision thickness gauges. Production is subject to factory quality controls, and every probe is tested before dispatch.

• Guaranteed compatibility with every instrument in the Dakota line
• Immediate availability from our 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

Can I use dual element probes with a precision thickness gauge?

No: precision thickness gauges (PMX, PCX, PZX) are designed for single element probes and do not recognise the pulse-echo format of dual element ones. For corrosion measurements on thin materials, consider our dual element transducers with a gauge from the CMX or MX line.

Which frequency should I choose to measure a 0.5 mm aluminium foil?

For sub-millimetre thicknesses on aluminium a 10-15 MHz single element probe with an acrylic delay line is recommended, paired with a PMX2-DL or PCX8-DL gauge. The delay line removes the overlap between the surface echo and the back-wall one.

What is the difference between contact and delay line tip in practice?

A contact probe measures directly above a minimum thickness threshold (typically 0.5 mm on steel). A probe with a delay line brings that minimum down to 0.127 mm on plastic and 0.15 mm on steel, but it requires a gauge that supports Interface-Echo Mode.

Do precision probes need to be calibrated differently?

Yes: single element probes require a more accurate two-point calibration than dual element ones, because small drifts in the velocity of sound produce larger percentage errors. Calibration on at least two reference thicknesses at the start of every shift is recommended.

Can I take corrosion measurements with precision probes?

Technically yes, but it is not recommended: on corroded or painted surfaces single element probes lose coupling. Dual element probes remain the right choice for corrosion inspection, even though they require dedicated gauges such as the CX, ZX, CMX or MX series.

---

Request availability and a quotation: contact us stating the model of your Dakota precision thickness gauge and the intended application.