
16
Secon 4: Genesis Control Opons and
Examples
The TraceNet system allows a variety of control opons for
heat trace operaon.
• Line sensing (RTD Sensor on pipe-wall)
• APC (Ambient Proporonal Control)
• Ambient Sensing (On-O Control)
The most energy ecient control mode is to use one (or
more) line sensing RTD’s for each heat trace circuit. When
using this control mode, the TraceNet Genesis panel will
have the RTD(s) connected to the DTM module in the
panel.
4.1: Line Sensing Control
When the RTD is directly sensing pipe-wall surface for
control, the key parameters are “Maintain Temperature” at
which the heat trace is energized or turned on. The “Max”
temp seng is where the heat trace will be de-energized,
or turned o. The dierence between these control sengs
denes the “dead band” (aka “control dierenal”)
From the line sensing RTD(s) the temperature of the
process line is read by the Genesis and is/are also able
to alarm for the user’s low and high temperature alarm
sengs. (A “high-high” temperature seng with circuit
“trip” opon is also determined from the RTD(s) placed
directly on the process line.)
Line sensing is the most energy ecient method of control
as the heat trace is only energized when the temperature
of the line is at the “Maintain” seng (or lower) and the
heat trace is de-energized when the it reaches the “Max”
seng, (aka “Maintain” plus “Dead Band”.)
4.2: Ambient Sensing Opons
Any ambient sensing control mode is less energy ecient
than line-sensing control, but generally allows fewer
heang circuits of longer lengths. This is because there is
no concern about process ow paths for heang circuit
layout, which will inuence RTD placement, the number
of sensors, and the number of heang circuits required.
For the TraceNet Genesis system, and its predecessor
the TCM18, “Proporonal Control” refers to a “me
proporoning” funcon for saving energy or more
accurately controlling maintain temperatures. So, if a given
situaon calls for 50% power, then the controller cycles on
and o 50% of the me to achieve this energy delivery.
There is a “Power Clamp” feature for these controllers that
is available when the controller is used with solid-state
relays, and is enabled when a circuit is set for “on/o with
so start”. This feature literally provides “so start” using
a reduced on/o duty me cycle of 1 second iniang at
the percentage selected.
There are two opons for Ambient Sensing with the
TraceNet Genesis System: Ambient Proporonal Control
and Ambient "On-O" Control.
4.2.1: APC (Ambient Proporonal Control)
With APC the heat trace will be set to operate at 100%
power (connuously on) at the minimum ambient
temperature, and reduce power as the ambient
temperature rises to the maintain temperature. When the
ambient temperature reaches the maintain temperature,
the heat trace produces no heat for that circuit. This
“Proporonal Control” is achieved by cycling the power
to the heat trace “on” and “o” so the me “on” is
proporonal to the dierence between the “Maintain”
and ambient temperatures. (Note: The minimum power
level is 8%, so that the electrical current and earth leakage
current levels can be accurately measured.)
Example of Ambient Proporonal Control (APC):
Maintain +40°F (+5°C) (i.e. to keep water from freezing) in a
minimum ambient condion of -40°F (-40°C) with APC control
method, follow this procedure:
The “Maintain” Temperature is set at +40°F (+5°C), at which
the heat trace would be de-energized, or “O”.
The “Minimum Ambient” temperature (at or below which
power is on 100%) would be programmed to be a value of
-40°F (-40°C).
(Note that the dierence between the Maintain and the
Minimum Ambient temperature denes the “Dead Band”,
across which the me “on” and “o” is established do deliver
the heat proporonally. The reduced power delivery results
in overall energy consumpon when compared to Ambient
“On-O” Control.)
APC control method can be successfully used for maintaining
elevated temperatures as well. This can reduce the number of
heang circuits by allowing longer heang circuits, but is not
as energy ecient as line sensing RTD temperature control.
The APC control method has tradionally been used only
with Solid State control relays because of rapid cycling of the
control relays during operaon. Now, by expanding the cycle
me between “on” and “o”, mechanical relays can be used.
“On/o with so start” is selected with 100% Power Clamp.
The result is that the circuit will operate in a normal on/o
method.
4.2.2: Ambient “On-O” Control
In this case the heat trace is fully “on” when the ambient
temperature falls below the “Maintain” temperature and
is fully “o” when the ambient temperature rises above
the “Maintain” plus the minimum control dead band.
Example of "On-O" Ambient Sensing Control:
As a third control mode opon, the TraceNet Genesis panel
may be congured for Ambient “On-O” Control. In this case,
one or two RTD’s may be used to sense ambient temperature,
typically in a shaded area subject to wind and rain in an area
convenient to the panel locaon.
In this case, the heat trace operates at 100% power whenever
the ambient temperature drops below the “Maintain”
temperature. To winterize water lines this is typically +40 to
50°F (+5 to 10°C). If the ambient rises above this value, plus
the minimum control dead band of +3° (°F or °C)) the heat
trace will turn o.