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CURRENT LOOP Q. i HAVE ATTEMPTED, JUST NEED CORRECTION OR REJECTION . THANKS

  • Thread starter Bazconway
  • Start date
  • #1
2
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1. Homework Statement

A 4-20mA current loop is being used to transfer temperature
values in the range + 10ºC to +60ºC.
(i) What temperature is represented by a current of 7mA?
(A) What current would you expect when the temperature of the
sensor is 32ºC?

Homework Equations


i HAD AN ATTEMPT, CAN U TELL ME IF ITS RIGHT. I AM REALLY STRESSED OVER THIS QUESTION. THIS IS MY 3RD ATTEMPT. tHANKS FOLKS


The Attempt at a Solution


20-4 =16mA
60-10= 50 DEGRESS

50/16=3.125

(A)
7mA-

3.125=X/7
X=21.88 DEGREES

(B)
32 DEGREES-

3.125=32/X

X=32/3.125

=10.24A
 

Answers and Replies

  • #2
33,518
5,196
1. Homework Statement

A 4-20mA current loop is being used to transfer temperature
values in the range + 10ºC to +60ºC.
(i) What temperature is represented by a current of 7mA?
(A) What current would you expect when the temperature of the
sensor is 32ºC?

Homework Equations


i HAD AN ATTEMPT, CAN U TELL ME IF ITS RIGHT. I AM REALLY STRESSED OVER THIS QUESTION. THIS IS MY 3RD ATTEMPT. tHANKS FOLKS


The Attempt at a Solution


20-4 =16mA
60-10= 50 DEGRESS

50/16=3.125
This is correct, but don't forget units. When you divide degrees by milliamps, what's the unit you get?
(A)
7mA-

3.125=X/7
X=21.88 DEGREES
I get a smaller value. For each 3.125 degree increment above 10 degrees, you need to add another mA to 4 mA.
(B)
32 DEGREES-

3.125=32/X

X=32/3.125

=10.24A
Your units are wrong, and the value is too small, by my calculations.

It would probably be helpful to derive one conversion formula for converting current in mA to temperature in degrees Celsius, and another to go the other way. The formulas you are using don't take into account that neither scale starts at 0.

See if you can get the equation of the line through these two points: (10 deg, 4 mA), (60 deg, 20 mA).
 

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