Application Note

Other switch tests
In the preceding step by step
description, the switch has been
removed from its operational cir-
cuit and the switch contact
closure is monitored to determine
state change.
You can perform this test with
the switch installed in its circuit.
In this instance, the switch con-
tacts will open and close and you
can use the 740 Series DPC to
measure the presence or absence
of system voltage (e.g. 120VAC) as
switch contacts change state. A
typical example would be measur-
ing the voltage applied to a
heater as controlled by the output
of the switch. The 740 series
DPCs can work with dc voltage in
addition to the continuity and ac
voltage examples previously
described.
Our examples in this applica-
tion note have been for
temperature switches. The 740
series DPCs allow you to test
pressure switches, too — in fact,
in 11 different engineering units.
Pressure switch tests are similar
to temperature switch tests — you
vary the process variable (source)
at the input, and monitor for a
change of state at the output. You
need to use a hand pump to
source pressure into a pressure
module and the switch. You can
manually document the results
by depressing the “Accept Point”
soft key when the test has been
completed.
With the 740 series DPCs, you
can source and measure many
key variables. And these tools are
useful for calibrating any process
switch. Of course, you will need
to supply your own inputs for
many types of process variables —
such as level, flow, and pH. The
principles of switch operation out-
lined here apply universally.
Fluke Corporation
PO Box 9090, Everett, WA USA 98206
Fluke Europe B.V.
PO Box 1186, 5602 BD
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etherlands
For more information call:
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ax [phone]
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Web access: http://www.fluke.com
©2004 Fluke Corporation. All rights reserved.
Printed in U
.S
.A
. 7
/2004 1263879 A-US-N Rev D
Fluke. Keeping your world
up and running
.
For detailed information on
calibrating pressure switches,
reference Fluke Application
Note 2069058.
5 Fluke Corporation Process and temperature switch applications with the 740 Series DPCs