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Frequently Asked Questions
| Q. How many detectors are required to
adequately cover my building? |
| A. The design and location of the
gas detector has much to do with the maximum area one detector can
properly cover. A correctly positioned and mounted Brasch gas
detector is designed to provide coverage over an area of 7000 to 9000
square feet when placed in a building with a ceiling height of 13 feet
or less. This area should be reduced to 5000 to 7000 square feet
when the detector operates in areas with ceiling heights greater than 13
feet. Detectors located in an area with restricted air flow, such
as an enclosed room, should be considered as only protecting that area. |
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| Q. Can a gas detector be calibrated
in the field? |
| A. Brasch gas detectors are
shipped to the customer fully calibrated. An existing sensor
cannot be calibrated in the field because conditions that affect the
calibration cannot be controlled. An otherwise functional detector
requiring recalibration can be restored to "like new" condition by
replacing the electronic board containing the sensor with a new,
calibrated sensor board assembly. This assembly is shipped to the
customer properly calibrated. Once installed, the detector can be
considered accurate within design parameters. |
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| Q. How long will my gas detector
operate before the sensor should be replaced? |
| A. Brasch electro-chemical gas
detectors use carbon monoxide sensors with a nominal lifetime of five
years. The nitrogen dioxide sensors have a stated nominal lifetime
of two years. Many detectors operate properly for periods
exceeding their published lifetimes. In the final analysis, the
lifetimes of the sensors depend heavily upon the amount of exhaust gas
to which the sensors are exposed. A sensor could be damaged beyond
use in a matter of hours if continuously exposed to undiluted exhaust
gasses. |
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| Q. What degree of accuracy should I
expect from a properly calibrated gas detector? |
| A. Gas detectors designed to
operate in automatic ventilating systems use three basic types of
sensors. Detectors using the older solid state sensors can obtain
an accuracy of +/- 10 percent of the full scale response. This
type of sensor is rapidly being replaced by the electro-chemical type of
sensor. This sensor can easily obtain an accuracy of +/- 5
percent of the full scale response. Some detectors use the "near
infra-red" principle of measurement to monitor the target gas.
This type of detector can obtain an accuracy of +/- 2 percent, and in
some cases, reach a short term accuracy of +/- 1 percent. The
"near infra-red" detectors are the most costly. Brasch gas
detectors use the electro-chemical type of sensor to obtain better than
required accuracy along with low cost. |
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| Q. How will I know when calibration
is necessary? |
| A. Other than applying a known
concentration of test gas to the gas detector, there is no tried and
true method of determining the condition of the sensor. Brasch
offers a test kit that can measure the response of GSE series carbon
monoxide detectors to a selectable gas concentration. However, like all
pieces of equipment, those who are familiar with the normal operation of
the unit will come to expect a certain level of performance. When
the detector appears not to react normally, it should be examined to
determine a cause. At that time, you may get some indication that
the sensor requires replacement. |
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| Q. Can Brasch gas detectors connect
to building management systems? |
| A. Most of the detectors produced
by Brasch have an output that can be connected to a building management
or control system. This output can be configured to send a linear
signal, proportional to the gas concentration, to the analog input of
the system. Most Brasch gas detectors permit field selection of either a
current or voltage signal. |
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| Q. Who may I contact for help with
installation or with questions concerning repair of a Brasch gas
detector? |
| A. Nearly all Brasch gas
detectors are sold through distributors. These distributors are
trained to answer most customer questions. Also, Brasch employs
service technicians that have been trained to answer any question that
may arise. Although the customer should include the distributor in
any discussion, the customer is encouraged to contact the factory
directly if necessary. Most questions can be answered over the
telephone. In rare cases where factory repair is required, the
detector can be returned to the customer within one or two weeks. |
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| Q. What assurance do I have that my
Brasch gas detector is properly calibrated when it leaves the factory? |
| A. Brasch calibrates all of their
gas detectors according to a procedure that has been developed to
provide a final accuracy within +/- 5 percent of full scale response.
This procedure requires at least six days. No detector is shipped
from the factory without first successfully passing this procedure.
All test gasses are analyzed to be within +/- 2 percent.
Calibration procedures are performed in a building constructed and
dedicated solely to that purpose. |
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| Q. Can carbon dioxide detectors be
used as a means to indirectly measure nitrogen dioxide? |
| A. In 1992 the U.S. Bureau of
Mines produced a study correlating the concentrations of carbon dioxide
and nitrogen dioxide gasses produced by a diesel engine. The study
concluded that once tuned and characterized using direct measurements,
the concentration of carbon dioxide could be used to indirectly
determine the level of nitrogen dioxide. This correlation,
however, was valid only for that specific engine in a closed system with
fixed operating parameters. This assumption would not be valid in
an open environment or with the presence of multiple engines.
Brasch strongly recommends that if a nitrogen dioxide source is present,
the concentration of this gas be measured with a nitrogen dioxide sensor
in order to obtain proper ventilation control. |
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| Q. Where can I obtain an operating
instruction manual for my Brasch gas detector? |
| A. Instruction/Operation manuals
for current and previous models are available in PDF format from this
web site. Links to documents for current models can be found in
the Literature section of the related detector page. Links to
documents for superseded models can be found in the Obsolete Literature
section of the Gas Detector Technical Information page. |
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| Q. How do I
activate the built-in self-test feature of the Brasch GSE and Onguard
models? |
| A. The Brasch Onguard and GSE
stand-alone detectors contain a feature which tests all detector
functions except for the sensor's response to the target gas. If
the ALM OFF/SELF-TEST front panel switch is pressed within five minutes
after power is applied, the detector will perform the self-test
function. The ventilation fans can be actuated by this self-test
feature if the fan is supplied with the proper operating voltage.
For a complete description of the self-test feature, please read the
Instruction/Operation manual. |
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| Q. Can I obtain
proper concentrations of test gasses for my detectors? |
| A. Most specialty gas companies
offer small containers of carbon monoxide mixed in air. These
tanks, when supplied with the proper regulator valve, can be used to
expose the detector's sensor to a test level of gas. Due to
numerous variables, the response to the test gas will only be
approximate. Brasch offers a test kit that can measure the
response of GSE series carbon monoxide detectors to a selectable gas
concentration. Test gas for Brasch carbon monoxide detectors should
have a concentration of between 50 and 100 PPM. Test gas for
nitrogen dioxide is not available in the 1 to 4 PPM concentration
required to test detectors with nitrogen dioxide sensors. The gas,
when mixed at these levels, will not remain stable within the tank long
enough to be of use. |
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| Q. Do carbon
monoxide and nitrogen dioxide produce homogenous mixtures in air? |
| A. Carbon monoxide has a
molecular weight of 28 grams per mol. Air has a molecular weight
of approximately 29 grams per mol. Carbon monoxide will
homogeneously mix in air. Nitrogen dioxide has a molecular weight
of approximately 46 grams per mol. This gas will tend to settle.
However, it should be noted that hot exhaust gas from a diesel engine
will initially rise, quickly cool and drift down to layer when mixed
with room air. |
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Electric heaters and gas detectors
