Controls Systems Problem Solving
Flow measuring transmitter
A flow measuring transmitter has a linear input-output graph just like the one shown in measuring transmitter graph. The input range is 0 to 10 liters per minute (L/min); the output range is 4 to 20 mA. Find the following:
1. Transmitter gain H, or Cm / C.
2. Equation for output Cm in terms of input C.
3. Output Cm when input C = 6 L/min
4. Input C when output Cm = 4 mA.
Solution flow measuring transmitter
Assumption : The graph of a flow measuring instrument is of the form Y = mx + C where Y = Cm , m = H and C = b.
A combination of amplitude gain + straight line equation + substitution method +process control diagram + Assumption.
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The graph for flow measuring transmitter is:
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The answer for flow measuring transmitter question no. 1 is H = 1.6 mA.min/litre and question no.2 is Cm = 1.6C + 4mA. Next find Cm and C.
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When input C = 6 L/min then output Cm = 1.6 x 6 + 4 = 13.6 mA When output Cm = 4 mA then input C = 0 |
Level measuring transmitter
A level measuring transmitter has a linear input-output graph just like the one shown in measuring transmitter graph. The input range is 5.0 to 10.0 meters (m), and the output range is 3 to 15 psi. Find the following:
1. Output Cm when input C = 6.3 m.
2. Input C when output Cm = 9.1 psi.
Assumption : The graph of a level measuring instrument is of the form Y = mx + C where Y = Cm , m = H and C = b.
Solution for level measuring transmitter is:
A combination of amplitude gain + straight line equation + substitution method +process control diagram + Assumption.
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The graph for level measuring transmitter is:
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When C = 6.3 metre, Cm = (2.4)(6.3) - 9 = 15.12 - 9 = 6.12 psi. When Cm = 9.1 find C.
9.1 = 2.4C - 9
2.4C = 9.1 + 9
C =
= 7.54 metre
Pressure measuring transmitter
A pressure measuring transmitter has a linear input-output graph just like the one shown in measuring transmitter graph. The input range is 0 to 200 kilopascals (kPa), and the output range is 10 to 50 mA. Find the following:
1. Output Cm when input C = 72 kPa.
2. Input C when output Cm = 13.7 mA.
Assumption : The graph of a pressure measuring instrument is of the form Y = mx + C where Y = Cm , m = H and C = b.
Solution for pressure measuring transmitter is:
A combination of amplitude gain + straight line equation + substitution method +process control diagram + Assumption.
Equation for pressure measuring transmitter is Cm = 0.2C + 10.
When C = 72 kPa, Cm = 0.2 x 72 + 10 = 24.4. When Cm = 13.7 mA then
0.2C = 13.7 mA - 10
C = 
= 18.5 kPa