Introduction
SRC Devices a world leader in design and manufacturing
of high quality reed switches, reed relays, proximity
sensors, and gas discharge tubes came to Cyth with the
proposal for a testing system of their reed switches.
SRC wanted to further become the industry leader as a
reed manufacturer by offering more specific and accurate
specifications, especially in terms of Operate and
Release measurements. Reed switches are switches that
are open or closed when a magnetic field is applied.
The device characteristics that were to be tested by the
system were the Operate, Release, Contact Resistance,
and Insulation Resistance. Cyth System has long worked
with National Instruments’ hardware, LabVIEW, and
TestStand, and knew the ease of configuration and
programming that it offered.
System Overview
A bowl feeder system was designed
by another company to
feed
in switches one at a time. The switches are
secured and probed by blocks and clamps controlled by
pneumatic actuators. When individual switches are
clamped, the different tests for specifications are
stepped through. The switches are then categorized and
dropped into individual bins through IAI Linear
Actuator.
Hardware
Operate/Release Test
When reed switches are secured and probed by pneumatic
actuators and clamp, the Operate and Release
characteristic test for the reed switch is first
tested. To apply a magnetic field to open and close the
switch, voltage is applied to a coil positioned around
the switch. In this application, NI PXI-4110,
Triple-Output Programmable DC Power Supply, was
extremely handy. Its 16-bit resolution offered the
accuracy desired to test the switches. Further, the
voltage and current readback/measurement functionality
of the PXI-4110 made it possible to know exactly what
magnetic field is being applied to the switch. To
detect the open and close of the switches, the NI
PXI-4070 FlexDMM is used.
Contact Resistance
Besides detecting the open and close state of the reed
switch, the PXI-4070 was also utilized for identifying
the contact resistance. The PXI-4070 was chosen for its
ability to utilize 4-wire to measure resistance and also
the PXI-4070’s Offset Compensated Ohms feature offered
more accurate reading of contact resistance.
Insulation Resistance
Insulation resistance characterizes the small current
leak of reed switch when the switch is in its open
state. Since the resistance is so small the PXI-4071,
7½-Digit PXI Digital Multimeter, was chosen for it
accuracy since the Insulation Resistance is minute. In
conjunction with the NI-4071, the PXI-4022, Current
Amplifier Module, was used for higher precision
measurement. The arrangement enabled the measurement,
in picoampere range with very little noise, of the
extremely small current that flowed through when voltage
is applied to the switch.
Mechanical Controls
At different points of the system, laser sensors are
used in conjunction with PXI 6514 Digital I/O module,
for the detection of reed switches as they move through
the system. The mechanical moving of reed switches
through the system is controlled through NI PXI 2568,
31-channel switch module. PXI 2568 turns on and off the
bowl feeder, feeding in one switch at the time, and then
also controls the pneumatic actuators when reed switches
are in position.
One innovation of the system is the Light Signal Tower
mounted on top of the system. The Light Signal Tower,
also controlled by the PXI 2568, has three different
lights (red, yellow, green) to convey the state of the
system to the operator. The future plans for the system
is to replicate it to a total of 24 systems. The Signal
Tower offers a visible and easy to understand method to
communicate the state of all the systems to the
operator. Red means the system requires immediate
attention; yellow means might need attention; and green
means normal operation. With Light Signal Towers in
place, a single operator can operate all systems single
handedly.
