PRESSURE MEASUREMENT

1.what are the difference between a dead weight tester and a gauge comparator ?

Dead weight tester is used for calibrating a test gauge. It works on the hydraulic principle, where as test gauge is compared with the standard dead weights n dead weight tester.

Gauge comparator: It is used for calibrating a pressure gauge against a test gauge. Calibration procedure is simple and quicker.

2.How would you select a pressure gauge for a process?

While selecting a pressure gauge for a process, consider the following points:

#Characteristic of the process (corrosive or non-corrosive)

#Operating pressure

#Maximum process pressure

#The gauge range should be a minimum of twice the process operating pressure.

PRESSURE GAUGE

3. Write the types of Bourdon tubes? Explain the purpose of different Bourdon tubes.

The following are the commonly used Bourdon tubes used in industries:

#Spiral –Low range 10 –100kpa

#C type –Medium range  100 – 5000kpa

#Helical – High range 5000 – 20000kpa

4.What is function of a hair–spring in a pressure gauge?

Hair–spring in a pressure gauge eliminates the Hysterisis (backlash/angularity) error caused in the quadrant (gear and pinion mechanism) and the weight of the pointer.

PRESSURE SWITCH

5.Name a few pressure switch manufacturing companies.

Barksdale, United electricals, don foss, CCS…etc.

6.What is the output of a pressure switch?

Output of an electric switch is a contact- open or close.

Out put of a pneumatic switch is a port operation- open or close, vent

7.How would you select a pressure switch for 500kpa Hi operation?

The following points are to be considered wile selecting a pressure switch for any process operation:

#The process operating pressure

#The maximum process pressure

#The process pipeline vibration

#The maximum working pressure of the pressure switch should be 2 times          greater then the maximum operating pressure

#The micro switch contact rating

#Process connection

#Local or remote mounting

8.Explain the contact selection on high and low pressure alarm switches? And explain why?

On a high pressure switch, the wiring is terminated on the “common” and the “normally close” contact terminals.

On a low pressure switch, the wiring is terminated on the “common” and the “normally open” contact terminals.

This type of contact termination is done to achieve a close contact from the switch during a normal (healthy) process condition which is a fail safe method.

9.What is to be done, if a transmitter gives a maximum output , where the transmitter range (jumper) is already in maximum selection?

Replace the capsule (sensor) for a higher range in the transmitter.

PRESSURE TRANSMITTER

10.Explain how to carryout a field zero check on a pressure transmitter?

1.If the transmitter signal is used for controlling, then put the controller on      manual.

2.Connect a digital multimeter in the current range in series with the transmitter output.

3.Isolate the process valve

4.Isolate the instrument isolation valve.

5.Open the equalising valve

6.Open the bleed valve and de-pressurise the transmitter.

7.Check for 4.00mA output signal, if not, adjust the zero screw.

BOILER PRESSURE TRANSMITTER

11.What-test equipment is required to calibrate a pressure transmitter in the field?

If it is a low range transmitter, then precision pneumatic test equipment like “wallace and tiernier” and pneumatic pump (or air supply) may be used.

If it is a high range transmitter, then a hydraulic pump and a test gauge is to be used.

PRESSURE SWITCH

PRESSURE GAUGE

12.What are pressure measuring/feeding test equipment?

The following are a few commonly used test equipment to measure and feed pressure: Tradinco, Wallance & tiernier, Ralston, Gauge comparator, Dead weight tester…etc.