Security Sales & Integration February 2022 - 16

SMARTS & PARTS
Tech Talk by Bob Dolph
Take Control
With Relays
▶ IF YOU'VE EVER HAD A SERIOUS
TOOL OF THE MONTH
Today's relays now include
" smart relays. " An example
is the EnerWave, which uses
Z-Wave Plus technology. This
dual relay module gets 50%
more wireless range and
energy effi ciency at 250%
faster processing and 400%
more memory. The smart
modules install and work
invisibly behind your existing
switches.
Correction: In the July 2021
Tech Talk, a paragraph explaining
the Ohm's Law calculation
should read: We can all agree
that the resistance (R) of the
cable in the problematic door
strike had increased due to
an increase in cable distance
and/or small wire gauge. The
doubling of the supply voltage
(E) would compensate for
this, and the current (I) for the
strike should now be adequate
to operate the door strike.
Bob Dolph has served
in various technical
management and advisory
positions in the security
industry for 30+ years. To
share tips and installation
questions, email Bob at
bdolph.ssi@gmail.com. Access
content from his 15+ years as
Tech Talk columnist by going
online at securitysales.com/
author/bdolph.
16
discussion with a professional athlete, you may
have asked them, " What is the most import
skill or discipline one needs to learn to succeed? "
Often you will hear them reply with,
" Learn and master the basics. " As with sports,
any profession has important basics that must
be taught and mastered in order to create a
solid professional career foundation. While
we have many new and exciting technologies
being presented to technicians every year, we
must not forget the importance of learning
and mastering the basics of our trade.
You have heard me talk about the importance
of basic skills in the past, and I thought it would
be appropriate to emphasize these technology
skills further this year. A note to all you old
timers out there - yes, much of what you read
may be old news, but it never hurts to review
the importance of sound basic skills and practices.
Many experienced techs are responsible for
training newbies. Do you make sure that they are
both understanding and practicing these basic
skills? Don't take it for granted that they will just
pick it up as they go along. Verbally test them to
see if they understand these important basics of
the trade.
I recently had a conversation with some senior
alarm techs. Th ey had commented that
many young techs lacked a true understanding
of application of relay devices. Yes, they knew
how to program the smart home controls, but
were confused when it came to properly and
safely connecting external devices using relays.
Over the years I have personally noticed this
confusion when auditing training sessions for
electricians.
When should I use a DPDT, SPST, NO/
NC, latching, delay or momentary relay? Simply
put, a relay is designed to switch devices
such as lights, automatic curtains, locks, AC
systems, or anything that typically has any
electrical load that is greater than the electrical
output of a control panel. Th e most popular
type of relay is still the electromechanical relay.
Security Sales & Integration FEBRUARY 2022
bdolph.ssi@gmail.com
Relays can provide isolation between circuits.
Th ough commonly used in our trade with DC
circuits, they can also be applied to AC circuits.
Th ey can be confi gured to provide logic
control using a design technique called ladder
diagraming.
Th e most basic relay is a small coil that when
presented with a voltage makes a pair of switch
contacts either open or close a circuit. Th is
would be a single pole, single throw, or SPST
relay. If the electrical contacts would be open
in the nonenergized state it would be classifi ed
as normally open, or a NO relay. If you have
two relay contacts operating from a common
contact you would have a single pole double
throw (SPDT) relay and one contact would be
NO and the other NC, operating on the same
common electrical trigger.
A bit of security trade trivia: Is a magnetic
reed door/window contact in an NC alarm
circuit considered a NO or NC device? It is a
NO device as it is activated by the accompanying
magnet. Remember the NO/NC state of a
relay is determined by its nonenergized state.
One word of caution when working with
electromechanical relays. Th e magnetic fi eld is
created by passing voltage through a small coil.
Th ere is a strange thing that happens with voltage
is suddenly removed from a coil. Th e electrical
collapsing of the coil's fi eld can induce
what is known as a reverse electrical magnetic
fi eld (EMF). Th is short but strong reverse voltage
pulse can be tens if not hundreds of times
greater in voltage. Th e pulse can damage electronic
circuits in the alarm panel controlling
the relay.
A standard method for preventing this potential
damage is to place a diode in parallel
across the relay input, allowing the diode to
clamp any reverse EMF from the collapsing
relay coil fi eld. An extra word of caution - if
you plan to have a relay confi gured to control,
say an inductive motor, make sure to have diode-type
devices, often called fl ybacks, in place
to prevent high current surges from damage
the relay contacts.
I have just touched the surface here on relay
technology, but I hope you now realize it is
important to dig further and truly understand
the devices you are working with in the fi eld.
You may want to take a further look at relays.
securitysales.com
COURTESY OF BOB DOLPH
http://www.securitysales.com/ http://www.securitysales.com
Security Sales & Integration February 2022

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