Answer / kunal singh dabi

A mains tester works because the potential difference
between the live and Earth makes a very small
(imperceptible) current flow through the tester and our
body to Earth. This current is just enough to light the
lamp / Neon. When you stick it in the Neutral socket, the
potential difference (just a volt or two, usually) is not
enough to give sufficient current to light the neon.When
the tester light glows, it mean electrons flow like,from
live terminal > tester > body > floor & walls of building >
inside the earth>goes back to the generator, via earth or
neutral conductor (Please note that somewhere, Neutral and
Earth are connected together so we have, in effect, a huge
loop of circuit.)

Above description is for AC supply only ( path complete
thorough earth or nutral to generator neutral), however
please note the fhilosophy is not applicable for DC supply
where - V is in floting condition (not grounded or earthed)
so due to un completation of that circuit tester light will
not glow.

Answer / kannan

there is a ballast resistor which is connected in series
with the testing terminal and the neon lamp, this limits
the current flow to the neon lamp, there to body & ground.
this is the one which protect you from electric shock. but
you cannot go on using the tester for any voltage. there is
voltage limitation, normally around few hundred volt, above
which you can get a shock.

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Q1: Consider part of a control loop, which excludes the transmitter, consisting of a process, a controller and a control valve which may be represented by two dead times of 0.5 min each and three exponential lags of 0.8 min., 1.0 min. and 1.5 min. respectively. We wish to express this system as an overall first order plus dead time (FOPLD) model ie gain, time constant and process dead time. (We will see later that this is often done, to simplify controller tuning). For this exercise, gain is considered to be 1.0. (A) If the transmitter is a flow transmitter whose behaviour can be described by a dead time of 0.2 min. and an exponential lag of 0.5 min. in terms of the overall dead time and overall first order lag how can the system behaviour be approximated ? Overall dead time = Overall time constant = (B) If the transmitter is a temperature transmitter with a temperature sensor in a protecting well whose behaviour can be described by a dead time of 0.7 min. and an exponential lag of 15 min. how can the overall system behaviour be approximated now? Overall dead time = Overall time constant =

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