Cable spacing as a means of noise mitigation

Separation distances

In situations where there are a large number of cables varying in voltage and current levels, the IEEE 518-1982 standard has developed a useful set of tables indicating separation distances for the various classes of cables.
There are four classification levels of susceptibility for cables.
Susceptibility, in this context, is understood to be an indication of how well the signal circuit can differentiate between the undesirable noise and required signal. It follows that a data communication physical standard such as RS-232E would have a high susceptibility, and a 1000-V, 200-A AC cable has a low susceptibility.

IEEE 518 – 1982 standard

The four susceptibility levels defined by the IEEE 518 – 1982 standard are briefly:

Level 1 (High) – This is defined as analog signals less than 50 V and digital signals less than 15 V. This would include digital logic buses and telephone circuits. Data communication cables fall into this category.

Level 2 (Medium) – This category includes analog signals greater than 50 V and switching circuits.

Level 3 (Low) – This includes switching signals greater than 50 V and analog signals greater than 50 V. Currents less than 20 A are also included in this category.

Level 4 (Power) – This includes voltages in the range 0–1000 V and currents in the range 20–800 A. This applies to both AC and DC circuits.

The IEEE 518 also provides for three different situations when calculating the separation distance required between the various levels of susceptibilities. In considering the specific case where one cable is a high-susceptibility cable and the other cable has a varying susceptibility, the required separation distance would vary as follows:

Both cables contained in a separate tray:

• Level 1 to level 2-30 mm
• Level 1 to level 3-160 mm
• Level 1 to level 4-670 mm

One cable contained in a tray and the other in conduit:

• Level 1 to level 2-30 mm
• Level 1 to level 3-110 mm
• Level 1 to level 4-460 mm

Both cables contained in separate conduit:

• Level 1 to level 2-30 mm
• Level 1 to level 3-80 mm
• Level 1 to level 4-310 mm.

The figures are approximate as the original standard is quoted in inches.

Click here to access the full article

Cable Glands For Full EMI Protection

Winning the war against electromagnetic interference (EMI) on today’s factory floors requires attention to detail. One of those details involves the ability of cable glands to contribute to a reliable grounding system.

Left unprotected, cable glands transmit electrical noise that can wreak havoc on motor-driven industrial processes. Many types of cable glands feature shielding to keep EMI at bay, yet the effectiveness of that shielding  can vary widely from product to product.

The ease of installation can vary as well. Some shielding options have difficult termination methods or grounding connections that can drive up labor cost and time.  

With SKINTOP^® MS-M Brush, our engineers have addressed both the shielding and installation issues. As its name suggests, this cable gland features a brush-type grounding connection that:

•  Enhances EMI control. Unlike other connection methods, such as the grounding clamps commonly used on drive systems, the brush provides continuous 360° contact around the cable’s screen braid. This continuous contact protects against EMI by lowering the resistance of current ground path and providing a low impedance connection between the cable shield and the housing.

•  Eases Installation. Making an EMI-free connection between cable and the SKINTOP cable gland is simple. Installers simply insert the cable, push the screen braid into the brush and tighten the cable gland assembly. Other grounding methods require far more effort to make the termination. Earth sleeves, for example, can serve as an effective grounding method, but their termination process requires precision measurements and exacting preparation of the stripped area.

In addition to its innovative brush-type connection, SKINTOP^® MS-M Brush offers IP 68 protection and resists temperatures up to 100ºC. Until recently, it was available only in metric sizes, ranging from M–25X1.5 to M–110X2.0. This month, we’ve introduced NPT sizes from ¾” to 2”.

Click here for detailed technical information on SKINTOP^® MS-M Brush

New Industrial Ethernet Cables For Tray Applications

Industrial Ethernet offers plenty of flexibility when it comes to designing complex automation networks.  Until recently, you couldn't say the same about data cables used in these networks.

CAT 5e Ethernet cables have traditionally been intended for stationary applications. And in the early days of industrial Ethernet, that limitation didn't matter much. Modern automation systems, however, increasingly require a new breed of Industrial Ethernet cables that can withstand more flexible conditions.

Our new ETHERLINE® Tray cable has been designed with flexibility in mind.  With its PLTC rating, the ETHERLINE® Tray can be used in cable trays, interconnecting the Industrial Platform with the Commercial Infrastructure.  The new ETHERLINE cable features four twisted pairs of stranded copper, and can handle gigabit speeds. 

Reliable Data Transmission.  Reliable data transmission is a must-have if you want to control production equipment over an Ethernet network. Unfortunately the electrical noise that pervades most manufacturing environments makes error-free data transmission a challenge. The new ETHERLINE cables combat electrical noise with a rugged, flex-friendly foil and braid EMI shield.

The construction of the ETHERLINE TRAY CAT.5e consists of a polyolefin-based insulation and a PVC jacket. The cable has a 600V rating making it ideal for tray applications alongside power cables. When used in flexible applications, the cable can withstand operating temperature from -25 to 80ºC.  They have a characteristic impedance of 100 Ω, ±15 Ω, at 100 MHz. 

Important Approvals. The new ETHERLINE cables have a wide range of approvals, which lets them serve in many different settings. These approvals include:

• CMR per UL 444
• CMG per UL 444
• PLTC per UL 13
• AWM 2570 80°C 600V
• c(UL) CMG
• RoHS II

Click here , For more information on the ETHERLINE CAT.5e Tray Cable

3 Conditions That Can Damage Your PLC

PLC in adverse conditions

In certain applications, the operating environment may have extreme conditions that require special attention or otherwise can seriously damage PLCs. These adverse conditions include excessive noise and heat and nuisance line fluctuations. This article describes these conditions and provide measures to minimize their effects.

1. Excessive noise
2. Excessive heat
3. Nuisance line fluctuations

1. Excessive Noise

Electrical noise seldom damages PLC components, unless extremely high energy or high voltage levels are present. However, temporary malfunctions due to noise can result in hazardous machine operation in certain applications. Noise may be present only at certain times, or it may appear at widespread intervals. In some cases, it may exist continuously.

The first case is the most difficult to isolate and correct.

Noise usually enters a system through input, output, and power supply lines. Noise may also be coupled into these lines electrostatically through the capacitance between them and the noise signal carrier lines.

The presence of high-voltage or long, closely spaced conductors generally produces this effect. The coupling of magnetic fields can also occur when control lines are located close to lines carrying large currents.

Devices that are potential noise generators include relays, solenoids, motors, and motor starters, especially when operated by hard contacts, such as push buttons and selector switches.

Figure 1 – Suppression of a three-phase motor lead

Analog I/O and transmitters are very susceptible to noise from electromechanical sources, causing jumps in counts during the reading of analog data. Therefore, motor starters, transformers, and other electromechanical devices should be kept away from analog signals, interfaces, and transmitters.
Although the design of solid-state controls provides a reasonable amount of noise immunity, the designer must still take special precautions to minimize noise, especially when the anticipated noise signal has characteristics similar to the desired control input signals.

IMPORTANT // To increase the operating noise margin, the controller must be installed away from noise-generating devices, such as large AC motors and high-frequency welding machines. Also, all inductive loads must be suppressed. Three-phase motor leads should be grouped together and routed separately from low-level signal leads.

Sometimes, if the noise level situation is critical, all three-phase motor leads must be suppressed (see Figure 1 above). Figure 2 illustrates line-filtering configurations used for removing input power noise to a controller or transmitter.

Figure 2 – Power noise reduction using one of three line-filtering configurations

Note 1 Keep line filters 12 inches or less from the controller. Minimize the line distance where noise can be introduced into the controller.
Note 2 To prevent ground loops, do not tie the common mode line metal case filters with other metal that is at ground potential. Doing so will reduce the filters’ effectiveness.

For the full article, click here