Installing Sensors Incorrectly As a Mistake #2 In Instrumentation

Four Sensor ‘Poors’ To Avoid

Generally speaking, there are four ‘Poors’ that can lead to incorrectly installing instrumentation sensors:

1. Poor placement
2. Poor control
3. Poor protection
4. Poor grounding

Each of above sensor ‘poors’ are described below, and by the way… have you read what is the mistake No.1 in an industrial instrumentation?

1. Sensor Placement

The best sensor can yield disappointing results if not installed correctly. Magmeters, for example, tend to generate noisy signals if the flow they’re measuring is turbulent. Bends, junctions, and valves in a pipe can all cause turbulence, thus magmeters work best when installed in sections of straight pipe.

Temperature sensors are also sensitive to placement. Even a highly accurate RTD tucked in the corner of a mixing chamber will only be able to detect the temperature of its immediate vicinity. If the mixing of the material in the chamber is incomplete, that local temperature may or may not represent the temperature of the material elsewhere in the chamber.

Local temperature issues are the classic mistake that home heating contractors often make when installing household thermostats.

A mounting location closest to the furnace may be convenient for wiring purposes, but if that spot happens to be in a hallway or other dead air space, the thermostat will not be able to determine the average temperature elsewhere in the house. It will only be able to maintain the desired temperature in its immediate vicinity. The rest of the house may end up roasting or freezing.

2. Controller performance // Poor control

Poor control also results when a sensor is installed too far away from the associated actuator. A distant sensor may not be able to measure the effects of the actuator’s last move in time for the controller to make an educated decision about what to do next.

Process of flattening hot steel

For example, consider the process of flattening hot steel into uniform sheets by means of two opposing rollers (see Figure 1 above). A thickness sensor downstream from the rollers gauges the sheet and causes the controller to apply either more or less pressure to compensate for any out-of-spec thickness.





Click here to access the full article

Selecting Wrong Sensor As a Mistake #1 In Instrumentation

Instrumentation issues

Despite ongoing advancements in measurement technology, instrumenting a process for feedback control remains a technical challenge. Today’s sensors are certainly more sophisticated than ever before, and fieldbus technology has simplified many installation issues considerably.
Nonetheless, much can still go wrong with an instrumentation project.

Selecting the wrong sensor

Technology mismatch //

Although it’s generally obvious what quantity needs to be measured in a flow, temperature, or pressure control application, it’s not always obvious what kind of flow meter, temperature sensor, or pressure gauge is best suited to the job.

A mismatch between the sensing technology and the material to be sensed can lead to skewed measurements and severely degraded control.

This is especially true when measuring flow rates. All flow meters are designed to measure the rate at which a gas or liquid has been passing through a particular section of pipe, but not all flow meters can measure all flows. A magnetic flow meter or magmeter, for example, can only detect the flow of electrically conductive materials by means of magnetic induction.

Non-conductive fluids like pure water will pass through a magmeter undetected. Magmeters also have trouble distinguishing air bubbles from the fluid in the pipe.
As a result, a magmeter will always yield an artificially high reading when bubbles pass through because it cannot sense the decrease in fluid volume caused by the presence of the bubbles. In a feedback loop, this occurrrence would cause the controller to throttle back the flow rate more than necessary, preventing the required volume of fluid from reaching the downstream process.

The problem gets even worse if the pipe is so full of air that it is only partially filled with liquid, a condition known as open channel.

Although recent technological innovations allow certain magmeters to work in such a challenging environment, mechanical sensors such as turbines yield artificially high readings, since a trickle of fluid will move the meter’s mechanism just as much as a full-pipe flow traveling at the same speed.

On the other hand, mechanical sensors are not affected by the conductivity of the fluid, so they will sometimes work where magmeters fail.

Click here to access the full article

12 Basic Motor Types Used For Industrial Electric Drives

Few Words About Electric Drives

Almost all modern industrial and commercial undertakings employ electric drive in preference to mechanical drive because it possesses the following advantages :

• It is simple in construction and has less maintenance cost
• Its speed control is easy and smooth
• It is neat, clean and free from any smoke or flue gases
• It can be installed at any desired convenient place thus affording more flexibility in the layout
• It can be remotely controlled
• Being compact, it requires less space
• It can be started immediately without any loss of time
• It has comparatively longer life.

However, electric drive system has two inherent disadvantages :

1. It comes to stop as soon as there is failure of electric supply and
2. It cannot be used at far off places which are not served by electric supply.

However, the above two disadvantages can be overcome by installing diesel-driven DC generators and turbine-driven 3-phase alternators which can be used either in the absence of or on the failure of normal electric supply.

Motor types for industrial electric drives

Ok, let’s take a short overview of twelve most basic motor types used for different industrial electric drives:

1. DC Series Motor
2. DC Shunt Motor
3. Cumulative Compound Motor
4. Three phase Synchronous Motor
5. Squirrel Cage Induction Motor
6. Double Squirrel Cage Motor
7. Slip ring Induction Motor
8. Single phase Synchronous Motor
9. Single phase Series Motor
10. Repulsion Motor
11. Capacitor start Induction run Motor
12. Capacitor start and run Motor

1. DC Series Motor

Since it has high starting torque and variable speed, it is used for heavy duty applications such as electric locomotives, steel rolling mills, hoists, lifts and cranes.

Click here to access the full article

7 Most Common Motor Enclosure Types Defined By NEMA Standards

Important role of enclosure

The enclosure of the motor must protect the windings, bearings, and other mechanical parts from moisture, chemicals, mechanical damage and abrasion from grit.

NEMA standards MG1-1.25 through 1.27 define more than 20 types of enclosures under the categories of open machines, totally enclosed machines, and machines with encapsulated or sealed windings.

The 7 most common types of enclosures are:

1. Open Drip Proof (ODP)

Allows air to circulate through the windings for cooling, but prevent drops of liquid from falling into motor within a 15 degree angle from vertical. Typically used for indoor applications in relatively clean, dry locations.

2. Totally Enclosed Fan Cooled (TEFC)

Prevents the free exchange of air between the inside and outside of the frame, but does not make the frame completely air tight. A fan is attached to the shaft and pushes air over the frame during its operation to help in the cooling process.

The ribbed frame is designed to increase the surface area for cooling purposes.

The TEFC style enclosure is the most versatile of all. It is used on pumps, fans, compressors, general industrial belt drive and direct connected equipment.

Total Enclosed Fan Cooled vs Open Drip Proof (TEFC vs ODP)

 

Click here to access the full article

5 Means Of Identifying Grounded Conductors (By NEC 200 Article)

Determining grounded conductors // NEC 200

Latest NEC requirements state at least five means of identifying grounded conductors. So, let’s go through each of them //

1. Sizes 6 AWG or smaller
2. Sizes 4 AWG or larger
3. Flexible cords
4. Grounded conductors of different systems
5. Grounded conductors of multiconductor cables

1. Sizes 6 AWG or Smaller

An insulated grounded conductor of 6 AWG or smaller must be identified by one of the following means //

1. A continuous white outer finish.
2. A continuous gray outer finish.
3. Three continuous white or gray stripes along the conductor’s entire length on other than green insulation.
4. Wires that have their outer covering finished to show a white or gray color but have colored tracer threads in the braid identifying the source of manufacture must be considered as meeting the provisions of this section.
5. The grounded conductor of a mineral-insulated, metal-sheathed cable (Type MI) must be identified at the time of installation by distinctive marking at its terminations.
6. A single-conductor, sunlight-resistant, outdoor-rated cable used as a grounded conductor in photovoltaic power systems, as permitted by 690.31 (article about permitted wiring methods), must be identified at the time of installation by distinctive white marking at all terminations.
7. Fixture wire must comply with the requirements for grounded conductor identification as specified in 402.8 (see below)
8. For aerial cable, the identification must be as above, or by means of a ridge located on the exterior of the cable so as to identify it.

Article 402.8 Grounded Conductor Identification – Fixture wires that are intended to be used as grounded conductors must be identified by one or more continuous white stripes on other than green insulation.

Click here to access the full article

SILVYN® Cable Track & Flexible Conduit

For applications that require added protection from mechanical or chemical stress, SILVYN® line of conduit offers the perfect solution. With a large selection of highly flexible metal or plastic conduit and matching glands, your installation has all round protection with the flexibility and bending capabilities required for any application. Whether it is indoor or outdoor, SILVYN® conduit has you covered!

SILVYN also offers a wide variety of cable tracks also known as cable chains. They are designed to maintain cables alignment in continuous-flexing applications. SILVYN® Cable Tracks increase the life of cable and hoses by protecting them from chemical wear and stress. The tracks are simple to assemble and install, reducing downtime, and greatly improving machine operation and appearance. SILVYN® Cable Track is resistant to oils, gasoline, and coolants.

SKINTOP HYGIENIC for Food & Beverage Applications

The new SKINTOP® HYGIENIC from Lapp Group is designed for food zone applications and prevents micro-organisms and bacteria from sticking to the surface. With an IP68/IP69 rating the gland can withstand high pressure and high temperature washdowns which makes it ideal for food & beverage applications.

13 Basic expressions often used in electrical testing

Testing of electrical installations

This is the simple list of basic terms you can often hear when testing and measurements of electrical installation (in general) is being performed. While expirienced electrical engineers will find this list short, I hope beginners will catch the essence and continue exploring this field of electrical engineering.
Feel free to suggest me an expression (along with description) you think it should be listed, it will be my pleasure to add it to the list and to move away from number 13

Ok, so here is the list:

1. Active accessible conductive part
2. Passive accessible conductive part
3. Electric shock
4. Earthing electrode
5. Nominal voltage
6. Fault voltage
7. Contact voltage
8. Limit Contact voltage
9. Nominal load current
10. Nominal installation current
11. Fault current
12. Leakage current
13. Short-circuit current

1. Active accessible conductive part

Active accessible conductive part is the conductive part of an electrical installation or appliance such as the housing, part of a housing etc. which can be touched by a human body. Such an accessible part is free of mains voltage except under fault conditions.

Switchboard contruction grounded (photo credit: ecsanyi)

2. Passive accessible conductive part

Passive accessible conductive part is an accessible conductive part, which is not a part of an electrical installation or appliance, like:

• Heating system pipes,
• Water pipes,
• Metal parts of air condition system,
• Metal parts of building framework
• etc.

Equipotential bonding of metal pipes (photo credit: diy.stackexchange.com)

Click here to access the full article

How to measure insulation resistance of a motor

Winding insulation resistance

If the motor is not put into operation immediately upon arrival, it is important to protect it against external factors like moisture, high temperature and impurities in order to avoid damage to the insulation. Before the motor is put into operation after a long period of storage, you have to measure the winding insulation resistance.

If the motor is kept in a place with high humidity, a periodical inspection is necessary.

It is practically impossible to determine rules for the actual minimum insulation resistance value of a motor because resistance varies according to method of construction, condition of insulation material used, rated voltage, size and type. In fact, it takes many years of experience to determine whether a motor is ready for operation or not.

A general rule-of-thumb is 10 Megohm or more.

Insulation resistance value	Insulation level
2 Megohm or less	Bad
2-5 Megohm	Critical
5-10 Megohm	Abnormal
10-50 Megohm	Good
50-100 Megohm	Very good
100 Megohm or more	Excellent

The measurement of insulation resistance is carried out by means of a megohmmeter – high resistance range ohmmeter. This is how the test works: DC voltage of 500 or 1000 V is applied between the windings and the ground of the motor. Ground insulation test of a motor

 

During the measurement and immediately afterwards, some of the terminals carry dangerous voltages and MUST NOT BE TOUCHED.

Now, three points are worth mentioning in this connection: Insulation resistance, Measurement and Checking.

Click here for the full article 

Electrical Thumb Rules You MUST Follow (Part 1)

Cable Capacity

• For Cu Wire Current Capacity (Up to 30 Sq.mm) = 6X Size of Wire in Sq.mm
  Ex. For 2.5 Sq.mm = 6×2.5 = 15 Amp, For 1 Sq.mm = 6×1 = 6 Amp, For 1.5 Sq.mm = 6×1.5 = 9 Amp
• For Cable Current Capacity = 4X Size of Cable in Sq.mm, Ex. For 2.5 Sq.mm = 4×2.5 = 9 Amp.
• Nomenclature for cable Rating = Uo/U
• where Uo = Phase-Ground Voltage, U = Phase-Phase Voltage, Um = Highest Permissible Voltage

Current Capacity of Equipment

• 1 Phase Motor draws Current = 7Amp per HP.
• 3 Phase Motor draws Current = 1.25Amp per HP.
• Full Load Current of 3 Phase Motor = HPx1.5
• Full Load Current of 1 Phase Motor = HPx6
• No Load Current of 3 Phase Motor = 30% of FLC
• KW Rating of Motor = HPx0.75
• Full Load Current of equipment = 1.39xKVA (for 3 Phase 415Volt)
• Full Load Current of equipment = 1.74xKw (for 3 Phase 415Volt)

Earthing Resistance

• Earthing Resistance for Single Pit = 5Ω, Earthing Grid = 0.5Ω
• As per NEC 1985 Earthing Resistance should be < 5Ω.
• Voltage between Neutral and Earth <= 2 Volt
• Resistance between Neutral and Earth <= 1Ω
• Creepage Distance = 18 to 22mm/KV (Moderate Polluted Air) or
• Creepage Distance = 25 to 33mm/KV (Highly Polluted Air)

Minimum Bending Radius

• Minimum Bending Radius for LT Power Cable = 12 x Dia of Cable.
• Minimum Bending Radius for HT Power Cable = 20 x Dia of Cable.
• Minimum Bending Radius for Control Cable = 10 x Dia of Cable.
•  

Insulation Resistance

• Insulation Resistance Value for Rotating Machine = (KV+1) MΩ.
• Insulation Resistance Value for Motor (IS 732) = ((20xVoltage (L-L)) / (1000+ (2xKW)).
• Insulation Resistance Value for Equipment (<1KV) = Minimum 1 MΩ.
• Insulation Resistance Value for Equipment (>1KV) = KV 1 MΩ per 1KV.
• Insulation Resistance Value for Panel = 2 x KV rating of the panel.
• Min Insulation Resistance Value (Domestic) = 50 MΩ / No of Points. (All Electrical Points with Electrical fitting & Plugs). Should be less than 0.5 MΩ
• Min Insulation Resistance Value (Commercial) = 100 MΩ / No of Points. (All Electrical Points without fitting & Plugs).Should be less than 0.5 MΩ.
• Test Voltage (A.C) for Meggering = (2X Name Plate Voltage) +1000
• Test Voltage (D.C) for Meggering = (2X Name Plate Voltage).
• Submersible Pump Take 0.4 KWH of extra Energy at 1 meter drop of Water.

Click here for full article

Basics of DC Motors For Electrical Engineers – Beginners

General about DC motors

Separate field excitation DC motors are still sometimes used for driving machines at variable speed. These motors are very easy to miniaturize, and essential for very low powers and low voltages.

They are also particularly suitable, up to high power levels (several megawatts), for speed variation with simple, uncomplicated electronic technologies for high performance levels (variation range commonly used from 1 to 100).

Their characteristics also enable accurate torque regulation, when operating as a motor or as a generator. Their nominal rotation speed, which is independent of the line supply frequency, is easy to adapt by design to suit all applications.

They are however less rugged than asynchronous motors and much more expensive, in terms of both hardware and maintenance costs, as they require regular servicing of the commutator and the brushes.

Construction of DC motor //

DC motor construction parts

A DC motor is composed of the following main parts:

Field coil or stator

This is a non-moving part of the magnetic circuit on which a winding is wound in order to produce a magnetic field. The electro-magnet that is created has a cylindrical cavity between its poles.

Armature or rotor

This is a cylinder of magnetic laminations that are insulated from one another and perpendicular to the axis of the cylinder. The armature is a moving part that rotates round its axis, and is separated from the field coil by an air gap. Conductors are evenly distributed around its outer surface.

Commutator and brushes

The commutator is integral with the armature. The brushes are fixed. They rub against the commutator and thus supply power to the armature conductors.



Click here for the full article

Where Do Electrical Faults Occur The Most?

Causes of electrical faults //

A fault is not a natural occurrence. It is an unplanned event which occurs unexpectedly. Electrical faults in an electrical installation or piece of equipment may be caused by //

• Negligence – that is, lack of proper care and attention
• Misuse – that is, not using the equipment properly or correctly
• Abuse – that is, deliberate ill-treatment of the equipment

If the installation was properly designed in the first instance to perform the tasks required of it by the user, then the negligence, misuse or abuse must be the fault of the user.

However, if the installation does not perform the tasks required of it by the user then the negligence is due to the electrical contractor in not designing the installation to meet the needs of the user.

Negligence on the part of the user may be due to insufficient maintenance or lack of general care and attention, such as not repairing broken equipment or removing covers or enclosures which were designed to prevent the ingress of dust or moisture.
Misuse of an installation or pieces of equipment may occur because the installation is being asked to do more than it was originally designed to do, because of expansion of a company, for example.

Circuits are sometimes overloaded because a company grows and a greater demand is placed on the existing installation by the introduction of new or additional machinery and equipment.

Click here to access the full article

What Would Be The Best Conductor Material for Electrical Cables

Al or Cu conductor…

The conductivity of copper is 65% higher than that of aluminium which means that the conductor size of similarly rated cables is proportionately smaller. Correspondingly less expense is then incurred in providing for insulation, shielding and armouring the cables themselves. Transport of the less-bulky cables is easier and so is installation. In limited spaces in cable ducts, the smaller volume and better ductility of copper cables can have an even larger benefit.

Copper cables are easily jointed because copper does not form on its surface a tough, non-conducting oxide. The oxide film that does form is thin, strongly adherent and electrically conductive, causing few problems.

Cleaning and protection of copper is easy and if joints are made as recommended they will not deteriorate to any great extent with age, which saves on maintenance costs.

HV copper cable (photo credit: businessinsider.com)

For the same nominal current rating, the cable with the aluminum conductor is significantly larger in diameter, carries a proportionally greater volume of insulation and is not so easily installed because of being less flexible. Aluminum is notoriously difficult to joint reliably. Table 1 compares aluminum and copper conductors for equivalent current rating.

Table 1 – Comparison between Copper and Aluminum Conductors in XLPE Insulated Steel- Wire Armoured Cables.

Characteristic	Copper 300 m2	Aluminum 500 m2
Overall diameter (mm)	66.5	83.9
Minimum bending radius (mm)	550	700
Max DC resistance/km at 20o C (ohm)	0.0601	0.0617
Approx. voltage drop/A/m (mV)	0.190	0.188
Continuous current rating, drawn in to duct (amp)	496	501

(Cable: to BS 5467 (& IEC 502) 4-core, stranded conductors, XLPE insulation, PVC bedding, steel wire armour, PVC oversheath, rated at 0.6/1.0 kV)

These notes have largely been derived from reference to BS 7450 which is identical to IEC 1059. Both of these give full details of the variables to be considered and the ways in which optimum cable size determinations can be made.


Click here to access the full article

Reliable cables for Drag Chain Applications