Why only proximity probe is having working voltage as -24v?

PROXIMITY PROBE:
        It uses NPN transistor, majority of other instrument uses floating voltage as +24 (due to PNP ).

control valve engineering job oriented questions

What is mean by CV of control valve?
   
    CV mean valve co-efficient or co-efficient of valve,which can be described as,
 Flow rate of water from inlet to outlet of control valve under the following condition condition

1. Valve open.
2. One PSI pressure on input and output.
3. Water at 60 Fahrenheit

 Unit of CV = US GALLONS/MINUTE.

  What you know about TRIM of control valve?

    All the contacting part of valve body with the process fluid.

                               OR

    All the removable part of valve body.

parts of cv

3D view of  cv 

Instrument interview related post

RTD on-site calibration

RTD calibration using temperature bath

parts of control valve

Alarm monitoring system

Instrument basics to be followed

megger

RF level switch

Colour combination of thermocouples

Temperature switch

instrument diagram( job scope oriented)

CV DATA SHEET

DPT DATA SHEET

INSTRUMENT SYMBOLS

HOOK-UP DIAGRAM

INSTRUMENT LOOP DIAGRAM

ILD

Interview oriented instrument pictures

MAGNETIC FLOAT LEVEL SWITCH

TUNING FORK LEVEL SWITCH

POINT LEVEL MEASUREMENT SWITCHES

instrumentation engineering useful images

DATA SHEET

LEVEL SWITCH

INSTRUMENT DATA SHEET

INSTRUMENT SYMBOLS