issue: September 2009 APPLIANCE Magazine
APPLIANCE Engineer - Ignition Systems
EMI and Gas Ignition: The Impact of Electrical Noise
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Gordon Swanson, general manager (Controls), Fenwal Controls
Gas-fired systems can benefit greatly
by using direct spark ignition (DSI), provided engineers know how to
address potential electrical noise challenges.
Figure 1. Before: Appliance wiring inducing EMI-related operational and reliability issues.
Direct Spark Ignition (DSI) is fast, straightforward,
and cost-effective, making it the method of choice for the majority of
gas-fired systems. But it is not without its challenges. Because the
DSI process works by creating a high-voltage spark, DSI controls
inevitably generate small to significant amounts of electromagnetic
interference (EMI), or “noise,” during their trial for ignition. This
electrical noise can interfere with both the ignition control and
nearby electronic components, affecting overall system performance and
Design for EMI
the effects of EMI can vary with environmental conditions and seemingly
small physical changes, EMI is not easy to observe or predict, making
it difficult to troubleshoot appliance performance. Proper system
design and installation consistency are crucial to avoid the need for
extensive (and expensive) testing and trouble-shooting both on the
assembly line and in the field. Fortunately, it is possible to create
reliable systems that minimize the naturally occurring noise created by
the lighting phase of the control.
Figure 2a. After: Appliance wiring using best practices to minimize EMI issues.
techniques used to effectively minimize EMI will depend upon the
available space and internal configuration of a given system. The main
considerations are cable length, cable type, cable positioning, and
grounding. To prevent generating excessive spark energy, engineers must
also consider the total time needed to light the burner.
high-voltage cables radiate electrical interference, direct-spark
installations should use the shortest practical cable length for the
specific application. This also has the added benefit of maximizing the
energy provided to the spark gap. Although they are more costly,
suppression-type spark cables are preferable to copper high-voltage
wires, as they significantly reduce noise emission. Keep in mind that
the resistive nature of suppression cables also reduces available spark
energy. Suppression cables should be kept as short as possible (less
than 60 in.).
Modern gas ignition controls are
not position-sensitive, so they should be mounted in the orientation
that facilitates the most direct wiring and shortest runs. High-voltage
and low-voltage cables should be run separately, and not cross over the
control or other electrical components and wiring.
high voltage and control cables must cross paths, make sure they do so
at right angles to minimize their contact with one another. Provide as
much air gap as practical. To reduce the possibility of signal
interaction, avoid long parallel runs and bundled wires. The shortest,
straightest distance to the control is always preferable.
appliances such as ovens and griddles that require more than one
ignition control system, install them as independent systems utilizing
the aforementioned best practices. Provide space between the controls
and orient them to allow optimal wiring configurations for each unit.
The power and ground to each control should be run separately—avoid
daisy-chaining—with each ground line tied back individually to a common
Other factors that can greatly affect the proper operation of a direct spark, or any ignition control system include:
a single path from each control to a common ground point. This avoids
ground loops, which are a common source of electrical noise.
and electrodes should have their own ground wire rather than relying on
sheet metal or pipe, which can loosen up or corrode over time.
that the common ground point is a solid, stable structure uninterrupted
by paint, hinges, or potentially unreliable mechanical connections.
spark cables should not be tucked against or lay directly on sheet
metal, as the energy will couple into the ground system, reduce spark
energy, and create noise. This is particularly noticeable on long
parallel cable runs along sheet metal surfaces.
burner system optimized to provide the shortest lighting time also
generates the least amount of noise. A system that takes 10 sec to
light creates more electrical interference than a system that lights in
- Once an ignition system design and
layout is finalized, provide detailed manufacturing documentation to
ensure correct installation in the finished product, resulting in
consistent performance in the field.
sure to include instructions for best practices regarding the external
wiring for power, communications, and other field-wired devices. Long
runs of unprotected connection wires, especially low-voltage control
wiring, can introduce losses or noise to the system. Where long runs
cannot be avoided, using an isolation relay or other control device is
an effective way to minimize potential field wiring issues.
noisy components on a separate power supply or transformer rather than
supplying the entire system from one source. This practice can help in
two ways: It may prevent noisy components from sharing wiring with
sensitive components, and, second, and it may allow all of the wiring
for the noisy component to be segregated in one smaller compartment of
Confirming Ignition System Performance
direct-spark applications will perform reliably when the design team
follows the best practices listed above. Regardless, it is important to
conduct thorough testing of each application under a variety of
conditions to validate system performance. These tests include but are
not limited to:
- Performance over the specified range of input voltages
- Performance over the expected range of spark electrode gaps
- Confirming performance at both cold-start and hot-relight conditions
- Testing with gas supply shut-off to confirm that no noise issues exist over the full ignition cycle through to lockout
- Accounting for expected production variations such as control placement, cable spacing, cable routing, or grounding
for any component issues related to variations from multiple suppliers
for high-voltage cable, electrodes, gas valves, etc.
- Testing of each system configuration over the entire model range.
reliable ignition systems for industrial and residential applications
requires adherence to best practices and thorough performance
validation. Often, the ignition system is an afterthought in the
combustion design process, and this can lead to unnecessary
manufacturing trouble-shooting, field issues, and customer
dissatisfaction. Utilizing a systems approach and working with controls
suppliers early in the design process is one way to reduce
manufacturing and service costs and result in reliable products that
consistently meet customer requirements.