Diagnostic tests and voltage measurements – Holtgreven Truck Scale Resources User Manual
Page 40
PT300 Users manual
Rev G, Feb 2011
Page 40 of 44
Diagnostic tests and voltage measurements
Charger voltage
Ensure the scale is off during the entire test. Remove the batteries and connect a meter across
the battery compartment observing correct polarity. Plug the battery charger in, the voltage
should measure 5.8V DC or more. Unplug the battery charger and reinstall the batteries.
Measure the voltage across the batteries. Depending on the state of charge on the batteries the
voltage should be between 3.6 to 5.8V DC. Plug the charger back in. The voltage across the
batteries should increase. If the correct voltage response is not observed, unplug the battery
charger. Remove one of the batteries and connect a meter, set to measure current to the battery
compartment connectors, observing correct polarity. Plug the battery charger in. The meter
should read between 25 and 75 mA DC.
Lamp
Cover the light sensor. The backlight should light up. Please note that it is difficult to see the
backlight in sunlight.
Keys
Press On/Off button, the scale should turn on. Press lb-kg, the scale should change units of
measure. Apply 50 lb to 250 lb to the scale. After you get a stable display, press the ZERO key.
The scale should go to a zero indication. Press the On/Off button and the scale should turn off.
Power down shutoff
Connect a variable supply to the input connector and remove the batteries. Connect the meter to
the positive battery lead. Set the supply to 6 V and turn the scale on. Reduce the input voltage
until the scale turns off. The voltage at shutoff should be between 3.2 and 3.5 Volts.
Load Cells
Each PT300 scale has two load cells. These load cells are the transducers that convert
mechanical energy (weight) to electrical energy.
Each load cell has 4 strain gages (700 Ω) and two temperature compensation thermistors. The
four strain gages are wired together to form a Whetstone bridge.
Schematic Diagram (typical values)
Excitation -
Excitation +
Signal -
Signal +
5
Ω
5
Ω
700
Ω
700
Ω
700
Ω
700
Ω