Ekranowany czy nieekranowany kabel pomiarowy: Który jest rzeczywiście potrzebny w Twojej aplikacji?

Wstęp

If you have ever dealt with unexplained signal noise on a production floor, you know how frustrating it can be.
Readings drift. Alarms trigger for no reason. Your team spends hours troubleshooting what turns out to be a cable
problem that could have been prevented from day one.

Problem ten zazwyczaj sprowadza się do jednej decyzji: kabel pomiarowy ekranowany czy nieekranowany?

At Tempsens, we get asked this question more than you would expect — and the answer is never just “go
with shielded.” The right call depends on your environment, your signal type, and what failure actually costs
your operation. Here is how to think through it.

Jaka jest faktyczna różnica?

At their core, both cable types carry low-voltage signals between sensors, transmitters, and control systems. The
difference is what sits around the conductors.

What Is Unshielded Cable?

Unshielded instrumentation cable is straightforward. You get insulated conductors twisted together and wrapped in an
outer jacket. The twisting of the pairs helps cancel out some interference through a principle called balanced
signal transmission, but the cable has no dedicated protective layer against external electrical noise.

What Is Shielded Cable?

Shielded instrumentation cable adds a metallic layer around the conductors — either a foil wrap (aluminium or
mylar), a braided wire mesh, or a combination of both. This shield acts as a barrier that either absorbs or
redirects electromagnetic interference (EMI) and radio frequency interference (RFI) away from the signal conductors.
The shield is then connected to ground at one end, giving stray electrical energy a controlled path to dissipate.

The result is a cable that keeps signal integrity intact even when the environment around it is electrically noisy.
Tempsens manufactures both types, and the team understands that signal integrity starts long before the cable
reaches the field.

Shielded vs Unshielded Cable: Side-by-Side Comparison

Types of Cable Shielding

Foil Shield (and the Drain Wire)

Foil shielding is an extremely thin film of aluminium or mylar material wrapped around the insulated wires in a way
that covers the entire wire with no overlap, making it excellent to provide shielding against radio interference at
high frequencies. However, the problem with this type of shielding is its limited flex life because the foil breaks
under repeated flexures and is therefore appropriate for fixed uses only. All the cables with this type of shielding
also have a drain wire that serves as a connection point for grounding.

Braided Shield

A braided shield is created with many fine strands of blank or tinned copper in a mesh pattern forming around
conductors. Coverage can be anywhere from 70% to 95% depending on the density of the braid, so there are still some
small holes as opposed to a foil shield that is continuous. Where braiding really excels is in terms of providing a
low-frequency electromagnetic interference protection and mechanical strength. The woven copper design allows for
better handling of the EMI produced by big motors, power transformers, and heavy switchgear compared to foil.
Additionally, this type of shield is capable of enduring many bends and vibrations without breaking, making it
suitable for any dynamic place.

Combination Foil + Braid Shield

Foil and braid combo have the conductors wrapped in foil first and then cover them with the braid on top. The foil
provides 100% electrostatic shield whilst the braid adds low-frequency EMI shielding as well as mechanical
protection in one construction. This is the requirement that the majority of industrial instruments are designed to
meet where analog signals are applied in the facilities with high-frequency noise and huge voltage machinery.

Even though the expenses may be considerable, the construction must be utilized if processes are of critical nature
because the idle signal alteration will incur serious repercussions in terms of safety and quality of the output.

Kiedy środowisko decyduje za Ciebie

Doświadczeni inżynierowie powiedzą Ci jedno: o wyborze kabla często decyduje otoczenie.

In a clean office building running a building management system, unshielded cable works well. There are no variable
frequency drives (VFDs), no high-power motors, no welding equipment generating magnetic fields. The signals are
transmitted correctly. The cost stays low. Installation is simple because unshielded cable is lighter, more
flexible, and easier to pull through conduit.

Step onto a refinery floor, a steel plant, or a water treatment facility, and the situation changes completely. Heavy
equipment cycles on and off constantly. Power cables run parallel to signal cables. There can be ground loops and
capacitive coupling between conductors. In these conditions, an unshielded cable will pick up electrical noise the
way an open microphone picks up background sound. Your 4–20 mA signal or thermocouple reading gets corrupted
before it even reaches the control panel.

Właśnie do takich warunków zostały zaprojektowane kable pomiarowe Tempsens.

Techniczny argument za ekranowaniem

Ekran w kablu pomiarowym spełnia dwie różne funkcje i obie są istotne.

Po pierwsze, blokuje zakłócenia elektrostatyczne. This comes from nearby power lines, lighting systems,
and high-voltage equipment. The shield acts like a Faraday cage — it surrounds the conductors and prevents
external electric fields from inducing stray voltages in the signal circuit.

Po drugie, zmniejsza efekt zakłócenia elektromagnetyczne from motors, VFDs, and switching power
supplies. While a foil shield handles electrostatic noise effectively, a braided shield performs better against
magnetic interference because of its lower resistance and better coverage. That is why high-demand applications
often specify a combined foil-and-braid shield — you get the best protection from both types of interference.

Proper grounding is non-negotiable with shielded cable. The shield must be grounded at one end only (typically at the
control panel or instrument end). Grounding at both ends creates a ground loop — a closed circuit that can
actually introduce the very noise you were trying to eliminate.

Grounding a Shielded Cable: Get This Wrong and the Shield Does Nothing

A shielded cable that is improperly grounded does not provide sufficient protection against noise. In fact, it can
even make matters worse. Improper grounding of shielded cables is one of the biggest problems faced in industrial
applications, but is quite easy to resolve.

• Grounding of a shield at one end only: Grounding of a shield should be done at one point only
  to allow stray electrical currents to dissipate without causing a short circuit between different grounding
  points.
• Grounding both ends causes a ground loop: When the shield is grounded both at the control panel
  and at the field instrument ends, any difference in ground potential causes unwanted currents to flow through
  the shield and create a new electromagnetic field.
• Control panel / receiver end grounding: For instrumentation cables, grounding should be done at
  either the control panel end or receiver end. This is considered standard practice for analog signal cables
  handling 4–20 mA signals, thermocouple, or RTD signals as well. The end of shield at field instrument end
  is kept ungrounded and insulated in order to avoid accidental contact with local ground.
• An ungrounded shield acts like an antenna: A shield having no grounding connection collects
  noise from the surroundings and has nowhere to send it. Instead of reducing the noise, it actually increases
  noise content around the wires to be protected.
• Continuity check after terminations: A shield that is grounded but which has a break along
  cable run can cause loss of effectiveness of the shield when such a break happens. In order to avoid such a
  situation, it is advisable to check shield continuity before putting the instrumentation loop in service.

Gdzie pasuje każdy typ kabla

Use Unshielded Instrumentation Cable When:

• Środowisko instalacji charakteryzuje się niskim poziomem narażenia na zakłócenia EMI/RFI.
• Pracujesz z sygnałami cyfrowymi, które są z natury bardziej odporne na zakłócenia.
• Najważniejszymi czynnikami są budżet i szybkość instalacji.
• Przebiegi kabli są krótkie i oddalone od kabli zasilających.

Use Shielded Instrumentation Cable When:

• Sygnały są analogowe (4–20 mA, termopary, czujniki RTD, wyjścia miliwoltowe).
• Kable biegną w pobliżu silników, napędów i linii wysokiego napięcia.
• Zastosowanie: przemysł naftowo-gazowy, petrochemiczny, farmaceutyczny i ciężki przemysł.
• Dokładność sygnału ma kluczowe znaczenie dla sterowania procesami i systemów bezpieczeństwa.

In most industrial instrumentation projects, shielded cable is the safer default. The cost difference between
shielded and unshielded cable is relatively small compared to the cost of diagnosing and fixing interference
problems after installation.

Słowo o kosztach i ryzyku

Unshielded cable costs less to buy, there’s no question about that. It is also quicker to install and easier to
terminate than other types. It makes perfect sense to choose this type of cable for some applications.

However, when you use signal cable in an electrically active environment, saving money on shielding cannot be called
an economical decision. Shielded instrumentation cable generally costs between 20 and 40% more than unshielded
cabling, depending on the type of shielding and the number of conductors. On paper, it seems a lot. In reality,
cable materials are never the largest item when it comes to costs of an instrumentation project.

The installed cost provides a fuller picture of comparatives between these two products. Often, the labour associated
with pulling, routing, and terminating the cable system costs more than the cost of the materials themselves. All
other costs in terms of tray, space, conduit fill, and time involved with shield termination must be added. In the
end, when calculating all of these costs, the difference between the shielded cable vs unshielded cable becomes
lesser than one assumed by most engineers. Risk calculation does not change, however. Cost of one troubleshooting
job in terms of technician time, downtime in the process, and possible product loss can exceed the cost of shielded
cable throughout the project.

The real question is not which cable is cheaper; the question is which cable offers better protection for your
process.

Podsumowanie

In short, both shielded and unshielded cable come with their unique advantages. However, choosing one or the other
will depend on a variety of factors, including your specific application and environment, the type of signal
transmitted through the cable, the distance the cable extends, and the possible consequences of signal loss on the
system in question.

As a general rule, unshielded cables are a good choice in low-interference environments with short runs of digital
signals. Conversely, if the signals that are transmitted in an industrial environment with lots of noise are analog
in nature, then choosing a shielded cable is the right thing to do.

Ensuring that you make the right choice at the specification stage can save a lot of time, money, and nerves as the
project goes on.

Key takeaways:

• While shielded cables does not always have to be used, in the world of analog measurement, it is almost
  impossible to avoid.
• The type of shielding of cables is important — foil, braided or combination shields have different
  abilities to block interference.
• One must ensure that the shielding is grounded correctly — a badly grounded shield may work worse than
  having no shielding at all.
• Total installed cost, not just the price of cable, determines whether the shielded type of cable should be used
  or not.

Explore Tempsens Instrumentation and Signal Cables

Tempsens produces a comprehensive range of shielded and unshielded instrumentation cables
designed for reliable signal transmission in the industrial, process, and hazardous locations. Whether you are
selecting cables for a new project or reviewing your existing systems, our technical experts can assist you in
choosing the right solution for your environment.

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