Ptg-3K Transducer Shooting - Cardinal GUARDIAN Owner's Manual

TROUBLESHOOTING, CONT.
PTG-3K Transducer
The Cardinal PTG-3K pressure transducer is a simple device to convert hydraulic pressure into a
voltage output that can be easily summed and trimmed. It can be checked much the same as a
standard strain gauge based load cell.
Figure No. 14 – PTG-3K Pressure Transducer
The PTG-3K is rated at 1mV/V. Because of this you will see exactly half of the output from the
transducer that you would normally see out of a 2mV/V load cell. The Transducer uses a
modified Wheatstone bridge circuit and uses Balco resistors for span temperature compensation
as well as copper alloy for zero temperature compensation.
To troubleshoot the PTG-3K you will first measure the resistance between the red and white
signal leads. This value should be from 340 ohms to 360 ohms. Resistance between the black
and green excitation leads will be from 402 ohms to 422 ohms.
Resistance from the circuit wires to the transducer body should be 5K Megohms (5 billion ohms)
Normally a standard VOM meter is not capable of measuring this resistance. A Megohmmeter
also called an Insulation Resistance Tester) is required.
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Since the PTG-3K will always have some amount of pressure on the gauged surfaces, it is
impossible to check the absolute zero balance condition of the transducer without removing the
transducer from the hydraulic circuit. This is something you normally will not want to do. When
the scale is first set up you should record the output of the transducer with the deck jacked up off
of the load cell. This value should be recorded and left inside the transducer cabinet so at a later
date you can compare the no-load output from the transducer to see if there has been a
significant shift in zero. A change of .2mV from the initial reading may indicate a change in the
sensor output.
If a sensor must be changed in the scale, first jack up the weighbridge at the corresponding load
cell to eliminate pressure from that circuit. Apply 2 wraps of Teflon tape to the new transducer
threads and force them all the way into the bottom of the threads. Remove the transducer to be
replaced, clean the manifold threads and check for loose Teflon in the manifold and install the
new PTG-3K. The sensor should be very tight in the manifold to avoid leaks. Bleed the circuit
and set the gauge gap in the cell and the scale should be ready to be calibrated.
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