Sodexo Food Solutions India Pvt Ltd interview questions and answers

Why we don’t use 2-20mA, 1-20mA, 3-20mA or 10-50mA signal instead of 4-20mA ?

Editor — Thu, 05 Aug 2021 07:07:00 +0000

Why we don’t use 2-20mA, 1-20mA, 3-20mA or 10-50mA signal instead of 4-20mA ?

Generally, in a transistor some amount of voltage is required for turning it on.
This voltage is the cut in voltage. Up to this voltage it exists a nonlinearity in its characteristics. Beyond this cut in voltage the characteristics of transistor is linear.
This nonlinear region lays between 0-4mA, beyond 4ma it linear. That’s why 4-20 mA range is used.

Due to some following reasons 4-20mA signal is used,

4-20mA has an inherent ‘live zero’. Zero engineering unit is 4mA not 0.0mA indicates an open circuit, fault in the line which is not valid.
4-20 mA has little, if any, signal loss in its circuit; current regulation compensates for minor resistances in terminal boxes, whereas voltage drop across resistances for voltage signals creates an error.
S 4-20 mA signal is less susceptible to noise pickup than a voltage circuit. So it is free from interference from other signals.
4-20 mA works at a relatively long distance(>1 Km ) boosting the power supply voltage will drive the signal further.

Editor — Thu, 05 Aug 2021 07:05:18 +0000

How to calculate the flow rate in Vortex flow meter ? What is K factor ? Can you give me an example calculation to understand the same as better ?

Vortex flow meters are flow sensors that detect the frequency of vortices shed by a bluff body placed in a flow stream.
The frequency of the vortices is proportional to the flow velocity.

Where:

f_v is the frequency of vortex shedding.
D is the diameter of the pipe.
w is the width of bluff body over diameter of pipe.
K is the a constant for all fluids given design of meter. A k factor is introduced to compensate for the non-uniform profile of pipe flow.
S is the Strouhal number, determined experimentally.

K-factor is a dividing factor.
The term is usually encountered when dealing with pulse signals although analog K-factors are sometimes used.

Editor — Wed, 04 Aug 2021 09:55:44 +0000

Temporary Change Control	Deviation
Change Control is a formal system by which qualified representatives of appropriate disciplines review proposed or actual changes that might affect a validated status.	Deviation is any deviation from documented procedure selected on purpose for temporary period to avoid unavoidable situation without affecting the quality and safety of product/procedure.
Change Control is a planned change after assessing the impact on the other functions.	Deviation is an unplanned change.
Temporary change means changing the approved procedure on temporary basis after risk analysis and evaluation by cross functional team.	Deviation means departure from any approved procedure unknowingly same like incident.

Editor — Wed, 04 Aug 2021 09:53:45 +0000

LOD is the loss on drying to test as per prescribed conditions which gives loss (presence) of all evaporating solvents along with water.
LOD test is used to estimate the Water & presented other volatile solvents.LOD is mainly preferable for the material with is Purified by solvents.
It is the dry base.