Transmitter calculation

1.Converting Linerar % to square root %

Square root % = sqrt(linear %)(10)

Example: Convert 50 % linear to square root

Square root mA           =          √A*10

                                   

                                   =          √50*10

                                  

                                   =          70.71%

2.Converting Linear mA to square root mA

                Square root mA                 =    √((A-4)/16 )x16)+4

                Where A is Linear mA

Example : Convert 12 mA linear to square root mA

               

                Square root mA                        =          √((A-4)/16 )x16)+4   

                                                             

                                                                =           √((12-4)/16 )x16)+4 

                                                               

                                                                 =           15.31mA

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instrumentation calculation 

 

LOCKED ROTOR CURRENT OF A MOTOR

LOCKED ROTOR CURRENT OF A MOTOR

The Locked Rotor Torque or Starting Torque is the torque the electrical motor develop when its starts at rest or zero speed. The magnitude of the Locked rotor current is determined by motor horsepower and design characteristics. Normally it will be 6 to 7 times of the Motor full Load current.

Normally Motor Name plate contains KVA code or Design Letter.

We can calculate the Locked Rotor Current Using the following Formula

Single Phase = (577 x HP x KVA/HP)/V

Three Phase= (1000  x HP x KVA/HP)/V

Find KVA/HP using the Following chart

CODE LETTER	KVA/HP RANGE	CODE LETTER	KVA/HP RANGE
A	0.00 – 3.14	J	7.10 – 7.99
B	3.15 – 3.54	K	8.00 – 8.99
C	3.55 – 3.99	L	9.00 – 9.99
D	4.00 – 4.49	M	10.00 – 11.19
E	4.50 – 4.99	N	11.20 – 11.49
F	5.00 – 5.59	O	12.50 – 13.99
G	5.60 – 6.29	R	14.00 – 15.99
H	6.30 – 7.09

Example:

Motor Name plate indicates phase 3,300 HP,4160 Volts,KVA Code G

LRC will be

(577 X 300 X 5.60)/4160 to (577 X 300 X 6.29)/4160

=232.02 to 261.73 Amps

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Instrument mA Conversion Calculator 

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mA Conversion Calculator