Keithley 7013-C, Instruction Manual

Page: 39 / 71

Operation
4-8
4.4.2 Activating external devices and circuits
The Model 7013 can be used to activate indicators,
alarms, relays and other external control circuits.
As an example, assume that a simple computer based
system is used to protect an expensive cutting tool on a
lathe. The cutting tool must be constantly lubricated to
keep it from burning up. The reservoir for the lubricant
has a sensor circuit (such as a float switch) to detect
when the lubricant level gets low. The sensor circuit is
connected to the input port of the Model 7001.
As shown in Figure 4-7, the protection system includes
a Model 7013 switch card which is used to control an
indicator, an alarm, and an AC power control circuit.
The illustration shows the state of the relays when the
lubricant level is normal. The indicator and alarm are
disabled, and the AC power control circuit is enabled.
When the lubricant level gets low, the appropriate
“low level” signal from the sensor circuit is detected
causing the computer program to branch to a subrou-
tine that will attend to the situation.
The program subroutine will close Channel 1 on the
switch card which activates an indicator on a control
panel alerting the operator that lubricant must be
added to the reservoir. If after a particular time period
the reservoir is not filled (level still low), Channel 2 will
close to activate an audible alarm to alert the operator.
If after another time period the lubricant level is still
low, Channel 3 will open. This will deactivate (open)
the relay which disables the AC power control circuit
causing the lathe to shut down and thus, saves the cut-
ting tool from being damaged.
CH 1
Indicator
Lamp
5V
7013
CH 2
12V
CH 3
30V
Alarm
Relay
AC
Power
Control
Circuit
AC Power
for Lathe
Figure 4-7
Controlling external devices and circuits