SmartControl™ Meter & TouchPoint™ 57 9E-926
Operation Instructions
Table 7: PRISM communication troubleshooting using a digital meter
Measurement Expected Reading Action
With DC power turned
off to all controls and
disconnected from the
SmartDairy™ Controller
measure the resistance
from the white wire to
the blue wire.
The resistance should
be 55 to 65 ohms.
• If the resistance is zero ohms then there is a
short between the white and blue wires. This
could be a connector that is in the wrong po-
sition, a loose strand shorting the wires or the
cable being pinched.
• If the resistance is 110 to 130 ohms then a
termination resistor is missing from either
end of the communication cable.
• There may be an open wire, loose connection,
a wire has not been installed in the connec-
tor and both termination resistors have been
installed. Repeat the resistance at both ends
of the communication cable
• If the resistance is less than 50 ohms but not
zero than there are too many termination re-
sistors installed.
With power turned on,
measure the voltage
across the white and blue
wires. The communica-
tion wires should be con-
nected to all controls.
The voltage should be
less than 0.1 volts DC
without communica-
tions occurring.
If the voltage is 0.5 volts or higher then a control
may be trying to communicate. Rest all controls
by turning power off for 30 seconds.
Measure the DC voltage
from the metal of the
parlor to the +24 VDC
output of the power sup-
plies. All communication
wires need to be discon-
nected from all controls.
The DC voltage should
be the same voltage
for what the power
supply is adjusted for.
If the voltage is less than 20 volts verify that
the minus connector of the power supply is con-
nected to earth ground.
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