Question

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5: In an open roof tank, the level transmitter side connected to the tank is: a: The high pressure side b: The low pressure side c: Either side can be connected to the tank 3: In an open roof water tank, the minimum water level is located 5 inches above the level transmitter. The maximum water level is located 50 inches above the level transmitter. The specific gravity of water is 1 A: The level transmitter should be set at how many inches of water to transmit 4 mA? B: The level transmitter should be set at how many inches of water to transmit 20 mA 6: In an open roof oil tank, the minimum oil level is located 5 inches above the level transmitter. The maximum oil level is located 50 inches above the level transmitter. The specific gravity of oil is 0.9. A: The level transmitter should be set at how many inches of water to transmit 4 mA? B: The level transmitter should be set at how many inches of water to transmit 20 mA?

Answer 1

Ans 5:

(a) The high-pressure side

The side of the level transmitter which is connected to the tank will be of high-pressure side and lower pressure side will be connected to the atmosphere. With these arrangements, level transmitter acts as a simple pressure transmitter. As shown in the figure:

HPTHG y LP-LawPren T- LEVEL 7RANSAINTEn HP oP EN TANK MEASUEPMENT

Differential pressure = P_high-P_low

The level transmitter is generally calibrated with and standard electrical output as given below:

4mA corresponds to the water level of 0% of the tank.

204mA corresponds to the water level of 100% of the tank.

Ans 3:

The following figure shows the given condition as the level transmitter is installed 5 inches below the minimum water level and 50 inches below to the maximum water level generally called suppressed zero installation. The specific gravity of water is 1.

LEVEL TRANS

A) Now to 4mA corresponds to the 0% water level of the water in the open tank. Therefore the zero suppression will be:

Calibration for 4mA = Zero suppression = SG * h.   Where SG is the specific gravity of the water.

Zero suppression = 1 * 5 inch.

B) Now 20mA corresponds to 100% water level of the water in the open tank.

Span = SG * H.    Where H = (H1-h)is the height of the water level.

Span = 1* 45 inch

Calibration for 20mA = zero suppression + span

= 5+ 45 = 50inches.

Ans 6: The same figure represents the conditions of this tank but here liquid is oil with specific gravity = 0.9

A) Now to 4mA corresponds to the 0% oil level of the water in the open tank. Therefore the zero suppression will be:

Calibration for 4mA = Zero suppression = SG * h.   Where SG is the specific gravity of the oil.

Zero suppression = 0.9 * 5 = 4.5inches.

B) Now 20mA corresponds to 100% water level of the oil in the open tank.

Span = SG * H.    Where H = (H1-h)is the height of the oil level.

Span = 0.9* 45 = 40.5inches.

Calibration for 20mA = zero suppression + span

= 4.5+ 40.5 = 45inches.