— The “Nervous System” of Industrial Automation Signal Transmission

In modern industrial automation systems, a large amount of analog signals, digital signals, and communication data must be transmitted from field devices to the control room. The key component responsible for this task is instrumentation cable.

Instrumentation cable is a type of cable specifically designed for transmitting low‑level signals. It is mainly used to connect field instruments (such as temperature transmitters, pressure transmitters, flowmeters, level gauges, actuators, etc.) with control systems (DCS, PLC, ESD, etc.). Unlike power cables, instrumentation cables do not carry high voltage or high current; instead, they precisely convey millivolt‑level, milliampere‑level weak signals or high‑speed digital data. Therefore, they require much higher performance in terms of anti‑interference capability, signal integrity, flame retardance, and other properties than ordinary cables.

1. Core Role of Instrumentation Cable

If we compare an automated control system to the human body:

• Sensors / transmitters are the eyes, ears, and skin — they perceive physical quantities (temperature, pressure, flow, level)

• Control system (DCS/PLC) is the brain — it processes information and makes decisions

• Actuators (control valves, motors, etc.) are the hands and feet — they execute commands

• Instrumentation cable is the nervous system — it transmits sensed signals accurately, completely, and in real time to the brain, and reliably conveys the brain’s commands to the hands and feet.

If the nervous system fails (signal loss, interference, attenuation, short circuit), the entire system becomes “disordered”. Minor issues cause reduced control accuracy; major failures can lead to production shutdowns or even safety accidents.

2. Main Structure of Instrumentation Cable

A typical instrumentation cable consists of the following components:

1. Conductor – Usually copper or tinned copper. Common sizes are 0.5 mm², 0.75 mm², 1.0 mm², 1.5 mm², etc. Conductors can be solid (single strand) or stranded. Stranded conductors offer greater flexibility, suitable for frequent movement or bending.

2. Insulation – Isolates conductors from each other and from the outside. Common insulation materials include:

• Polyethylene (PE) – low dielectric constant, good signal transmission

• Cross‑linked polyethylene (XLPE) – better heat resistance

• Polyvinyl chloride (PVC) – low cost, used in general applications

• Fluoroplastics (FEP/PFA) – high temperature and corrosion resistance, used in harsh environments

3. Pair shielding (for multi‑pair cables) – Two cores are twisted into a pair to transmit one differential signal or one analog signal. Twisting reduces magnetic interference. Pair shielding (aluminum foil/polyester tape) wraps each pair individually to prevent crosstalk between pairs.

4. Overall shield – Wraps all pairs or singles together to resist external electromagnetic interference. Shielding types include:

• Overall aluminum foil

• Overall copper wire braid (coverage typically ≥80 %)

• Combined foil + braid

5. Inner sheath (optional) – Covers the overall shield and provides mechanical protection.

6. Armor (optional) – Galvanized steel wire braid or steel tape wrap, used for direct burial, high mechanical stress, or rodent/termite protection.

7. Outer sheath – The outermost protection. Common materials include:

• PVC – general purpose

• Low Smoke Zero Halogen (LSZH) – flame retardant, low smoke, non‑toxic; used in crowded or confined spaces

• Oil‑resistant PVC – used in oil & gas, chemical plants, and other oily environments

• Polyethylene (PE) – good water resistance, used for direct burial

3. Common Types of Instrumentation Cable

Depending on the application and signal type, instrumentation cables are mainly divided into the following categories:

4. Key Performance Indicators for Instrumentation Cable

When selecting instrumentation cable, pay attention to the following parameters:

• Shielding coverage – Braid shielding typically requires ≥80 %, and ≥90 % for demanding applications. Shielding effectiveness directly affects electromagnetic interference immunity.

• Capacitance (pair‑to‑pair, pair‑to‑shield) – Low capacitance is critical for long‑distance analog signal transmission and intrinsically safe circuits.

• Characteristic impedance – For digital bus cables (e.g., RS‑485), characteristic impedance should be 120 Ω ± 10 %; otherwise, signal reflections occur.

• Flame retardance rating – Meets IEC 60332‑1 (single vertical burn) or bunched flame retardance Class A/B/C.

• Fire resistance rating – Circuit integrity time under flame (e.g., 750 °C × 90 minutes).

• Operating temperature range – Ordinary PVC: ‑20 °C to 70 °C; PE: ‑40 °C to 80 °C; fluoroplastic: ‑60 °C to 200 °C.

• Oil and chemical resistance – For chemical plants, refineries, and other environments with oil or corrosive gases, the jacket must resist oil and chemicals.

• Intrinsic safety parameters – When used in hazardous explosive zones, the cable’s distributed capacitance and inductance must meet relevant standards to match with associated IS apparatus.

5. Selection Guidelines for Instrumentation Cable

Different industrial scenarios have very different requirements for instrumentation cable. Selection should consider:

1. Signal type – 4‑20 mA analog, thermocouple/RTD signals, digital communication (RS‑485, HART, Profibus)?

2. Installation environment – Conduit, cable tray, direct burial, overhead? Risk of mechanical damage (rodents, crushing)?

3. Ambient temperature – Normal, high, low?

4. Chemical corrosion – Exposure to oil, acid, alkali, solvents?

5. Fire protection – Does it require flame retardance, fire resistance, low smoke zero halogen?

6. Hazardous area – Is it located in Zone 0/1/2? Does it need intrinsic safety cable?

7. Electromagnetic interference – Are there VFDs, large motors, RF equipment nearby? Is high‑grade shielding needed?

8. Transmission distance – For long distances, consider capacitance, attenuation, and signal bandwidth.

6. Why Choose Tiankang Instrumentation Cable?

Anhui Tiankang (Group) Co., Ltd. has nearly 50 years of experience in the R&D and manufacturing of wires, cables, and instruments. We are one of the few large‑scale groups in China that possesses integrated production capability for both instruments and specialty cables. Our instrumentation cables offer the following advantages:

• Complete product line – Covering general instrumentation cable, computer cable, IS cable, bus cable, compensating cable, high‑temperature cable, armored cable, and more.

• Strict quality – Certified under ISO 9001, ISO 14001, GJB 9001B. Our products carry the “National Exemption”, “CCC Certification”, and “China Well‑known Trademark” designations.

• In‑house testing capability – CNAS‑accredited laboratory where product performance is validated under simulated operating conditions.

• Industry experience – Widely used in oil & gas, petrochemicals, coal chemicals, power, metallurgy, pharmaceuticals, water treatment, and other fields. Long‑term supplier to CNPC, Sinopec, CNOOC, and many large enterprises.

• Customization services – We can produce special cables according to customer drawings or samples, including non‑standard pair counts, special jacket materials, and unique armor constructions.

• Global supply – Exported to more than 40 countries and regions, including Russia, Iran, Kazakhstan, Saudi Arabia, Italy, and Brazil.

Whether you need intrinsically safe cables for oil & gas platforms, high‑temperature oil‑resistant cables for refineries, or RS‑485 bus cables for digital factories, Tiankang provides professional and reliable instrumentation signal transmission solutions.

Contact Us

For more information about instrumentation cable products or to request a quotation for your project, please email [email protected] or visit http://www.tiankang-global.com/. The Tiankang Electrical Engineering Technology Department is ready to assist you.