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Electrical Engineering
Electrical engineering is a field of engineering that deals with the study and application of electricity, electronics and electromagnetism.
23,056 Questions
The generated angle between phases in a three phase system is 120 degrees.
What is the CMRR measuring circuit for signal conditioning module with current output?
CMRR (Common Mode Rejection Ratio) it is a parameter normally associated with operational amplifiers or differential inputs. The importance of a good CMRR is to cancel unwanted noise signals which are the same on the two input signals. For any form of signal conditioning it would be an important parameter, since the idea of signal conditioning is to be able to provide a pure signal and as little noise and error as possible.
Basically an operational amplifier has a differential input. It means that the difference between two inputs is amplified and that what is similar gets rejected. In a very simplified way we can say. If I have 5V on one input and 3V on the other then 3 volt will be rejected and not being looked at and the 2V difference will continue through the amplifications stages.
But in real life no operational amplifier or differential input stage is perfect and there is always some form of error. One type of error is where not all the common voltage (the 3V part) is rejected or cancel entirely. A small amount still go through, allowing noise to be amplified. The CMRR parameter exist in two forms. 1) factor 2) factor in the decibels (lowercase!! since deci means x10-1)
Before we really know what the CMRR factors in their numerical values mean. Lets look at the composition of the factor.
Aol= Open Loop Voltage Gain = The amount of times the output voltage is more than the difference in input voltage, if no feedback is used. Usually in the order of 100 000 or so but may vary allot depending on the design of the amplifier
Acm= Common Mode Voltage Gain = The amount of times the output is more than the input, if both input voltages are exactly the same. Typically in the order of 0.2
CMRR = Aol/Acl
Example: = 100 000/0.2 = 500 000
Now we understand where the logic of using the decibel scale come in. It is unnecessary to work with values like 500 000 for a parameter like that. Then we rather say:
CMRR = 20.Log (Aol/Acl ) and it is then 114dB where dB is the unit of decibel. Remember that 500 000 does not have a unit, it is only an factor. If you have a factor in dB form, then:
Aol/Acl=10(CMRR/20)
Example:
5.7=113.98dB / 20
500 000=105.7
The amplifier provides maximum gain to the differential signal and the amplifier give minimum gain to (unwanted) common mode voltage and actually reducing its value on the output by 5 times (x 0.2) this means that common mode noise may be reduced by 5 times while a differential signal can be amplified by 100 000 times. All we need to understand is that CMRR is the ratio between closed loop gain and common mode gain.
The bigger the CMRR is the better.
CMRR is not the only parameters that effect error and noise.
Consider some more effects, not all the effects will be shown on datasheets and often we should hope, trust and assume the parameter will be good enough for our application. It is likely that the following effects may be affected by circuit components around the inputs such as differential inputs, feedback, filters ext. Therefore the interface to a module may not reflect the same values as given. But for many that do make use of operational amplifiers or differential stages will have the following effects somewhere in the module if not directly at the input:
*Input offset voltage:
Caused by slight differences between the base-emitter voltages of the differential input stage and can go up to a few mV
*Input bias current
The average of both input bias currents of the input stage. Bias current is required to get input stage transistors operational and can be about 500nA depending on the design. The type of signal source and conditioner will determine what effect it will have on the precision.
*Input offset current
The absolute value of the difference between bias currents.
*Input impedance
The input impedances for differential and common mode may differ. If transducers with internal resistance are used, like a load cell for instance. Then the changes in impedance may have an effect on the amount of error. The common mode impedance is the impedance of each input to the ground. Differential impedance is the impedance between the two inputs. Impedance may be anything depending on the type of conditioning circuits. But it can go up to the order of mega ohms and depending on design and application might not effect the output much.
*Temperature coefficient
The effect temperature have on the device. The parameter will indicate the amount of offset that may occur due to the change in ambient temperature. Although the values are often in the uV/°C bare in mind the application. Some applications might require precision of up to 12 000 divisions of its full scale deflection or capacity and in that case, expecting a resolution of 3uV per division is possible.
* Nonlinearity
The amount of deviation from the proportional input to output ratio over the entire operating range.
How applicable the above arguments are to the signal conditioning systems will depend on the type of design and for what type of signals the conditioner is developed for. They may differ allot from one application to the next. Therefore the explanation is more based on the typical operational amplifier or differential stage what the question about CMRR would be applicable to. This answer will apply to more applications than only signal conditioners.
Some signal conditioners may be time or logic based inputs and would not require the functionality of operational amplifiers.
What is GD square mentioned on the Motor?
The GD square that is mentioned in motors is also called the flywheel effect. It is usually used in most of the industrial applications and processes.
Difference between voltage and emf?
'Voltage' is simply another term for 'potential difference', and an electromotive force is the open-circuit, or no-load, potential difference of a source such as a battery or generator.
Example component use integrated circuit?
(I am assuming you are asking "What are some examples of devices that use Integrated Circuits?") Note that an Integrated Circuit (IC) is normally regarded as a "component" itself. ICs are used in virtually every electronic device found today including, but by no means limited to: MP3 players, Computers, Computer Peripherals, TVs, DVRs, Radios, Cars, Microwave Ovens, and on and on ... hopefully you get the idea.
What is knee point voltage of current transformer?
10 % increase in voltage gives you 50 % increase in excitation current is called knee point voltage. To measure this first demagnetise the CT and apply voltage gradually from secondary keeping primary winding open circuited. while doing this above phenomeneo will be obsesrved.
What is advantages and disadvantages of SCR?
Advantages: simple turn On Latcing device, turn ON gain is very hih, low cost,Hih voltage and high current device. Disadvantages: Low switching speed, most suited for line commutated applications betwee 50 and 60 Hz can not be turn off with gate controlled. From: N.G.PATEL(UPS)B.TECH.(ELECT)
How do you calculate percent modulation of an AM wave form?
%m = Ei/Ec *100 or % m= V max -V min/Vmax+Vmin * 100
What is Power systems protection?
Primary and back-up protectionThe reliability of a power system has been discussed in earlier sections. Many factors may cause protection failure and there is always some possibility of a circuit breaker failure. For this reason, it is usual to supplement primary protection with other systems to 'back-up' the operation of the main system and ensure that nothing can prevent the clearance of a fault from the system.
Back-up protection may be obtained automatically as an inherent feature of the main protection scheme, or separately by means of additional equipment.
Time graded schemes such as over current or distance protection schemes are examples of those providing inherent back-up protection; the faulty section is normally isolated discriminatively by the time grading, but if the appropriate relay fails or the circuit breaker fails to trip, the next relay in the grading sequence will complete its operation and trip the associated circuit breaker, thereby interrupting the fault circuit one section further back. In this way complete back-up cover is obtained; one more section is isolated than is desirable but this is inevitable in the event of the failure of a circuit breaker.
Where the system interconnection is more complex, the above operation will be repeated so that all parallel infeeds are tripped.
If the power system is protected mainly by unit schemes, automatic back-up protection is not obtained, and it is then normal to supplement the main protection with time graded over current protection, which will provide local back-up cover if the main protective relays have failed, and will trip further back in the event of circuit breaker failure.
Such back-up protection is inherently slower than the main protection and, depending on the power system configuration, may be less discriminative. For the most important circuits the performance may not be good enough, even as a back-up protection, or, in some cases, not even possible, owing to the effect of multiple infeeds. In these cases duplicate high speed protective systems may be installed. These provide excellent mutual back-up cover against failure of the protective equipment, but either no remote back-up protection against circuit breaker failure or, at best, time delayed cover.
Breaker fail protection can be obtained by checking that fault current ceases within a brief time interval from the operation of the main protection. If this does not occur, all other connections to the bus bar section are interrupted, the condition being necessarily treated as a bus bar fault. This provides the required back-up protection with the minimum of time delay, and confines the tripping operation to the one station, as compared with the alternative of tripping the remote ends of all the relevant circuits.
The extent and type of back-up protection which is applied will naturally be related to the failure risks and relative economic importance of the system. For distribution systems where fault clearance
Times are not critical, time delayed remote back-up protection is adequate but for EHV systems, where system stability is at risk unless a fault is cleared quickly, local back-up, as described above, should be chosen.
Ideal back-up protection would be completely independent of the main protection. Current trans-formers, voltage transformers, auxiliary tripping relays, trip coils and D.C. supplies would be duplicated. This ideal is rarely attained in practice. The following compromises are typical:
a. Separate current transformers (cores and secondary windings only) are used for each protective system, as this involves little extra cost or accommodation compared with the use of common current transformers which would have to be larger because of the combined burden.
b. Common voltage transformers are used because duplication would involve a considerable increase in cost, because of the voltage transformers them-selves, and also because of the increased accommodation which would have to be provided. Since security of the VT output is vital, it is desirable that the supply to each protection should be separately fused and also continuously supervised by a relay which will give an alarm on failure of the supply and, where appropriate, prevent an unwanted operation of the protection.
c. Trip supplies to the two protections should be separately fused. Duplication of tripping batteries and of tripping coils on circuit breakers is sometimes provided. Trip circuits should be continuously supervised.
d. It is desirable that the main and back-up protections (or duplicate main protections) should operate on different principles, so that unusual events that may cause failure of the one will be less likely to affect the other.
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What compose a transformer substation?
A transformer substation comprises of transformation equipment- the transformers, the accessories for the connection of the transformers to the HT Lines (Primary Input)- usually concrete poles/steel towers, insulators etc; normally two or more transformers are present to allow maintenance and faults without the supply being interrupted.
2. The substation protective equipment such as lightning Arresters, Line Fuses and Breakers, Isolators (as appropriate)
3. Effective Earthing system and equipment
4. The Distribution equipment such as feeder pillar units, busbars etc depending on the type of transformer substation.
What is the abbreviation for volts?
V. Voltage is also sometimes abbreviated E, usually in Ohm's Law equations. The E stands for electromotive force.
yes it would still be balanced
balance depends only upon the other four resistors not the one in the middle
How do you calculate how hot a wire can get?
Determine what the wire is made of and look up the melting point of that metal. Once it reaches that temperature it will not be wire anymore but molten metal.
What is the analogy of short circuit?
Im searching for the analogies of the following words 1.Overloading 2.Short circuit 3.Circuit Protectors 4.Electromagnetic Induction 5.Len'z law
What does the term house load mean?
In an apartment building power is used to keep the building hallway lights and plugs operational. Run ventilation systems, heating. Anything that the building needs in the way of electrical services that is not associated with the apartments. This way the apartment owners are not paying for power being used by the building. This building demand load is known as the house load.
What are the advantages and disadvantages of UJT?
The advantages of a UJT include low cost, a negative resistance characteristic, and a low value of triggering current. The main disadvantage is the inability to provide decent amplification.
What is capacitive power generation?
I saw the question and came here hoping for a answer and not to answer
What is d-q coordinate of IPM machine?
d-q a direct (magnet pole) and quadrature (90deg out of phase electrically) axis. This is identical to surface permanent magnet machine (SPM).
