DayTronic 5M78 Manual - Página 12

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4. VERIFICATION OF NORMAL OPERATION

It is the purpose of this section to aid the user in determining, in the event of a

malfunction to which the Model 5M78 is suspected of contributing, whether the

instrument is functioning normally or whether it is the source of the observed

trouble. In the event the unit requires repair, the user may also contact the

factory Service Department or the local Daytronic Representative for assistance.

Daytronic service information is located on the last page of this document.

If the instrument is suspected of faulty operation, follow the steps below.

(a)

If the unit is totally inoperational (front-panel power indicator does not

light), check the primary power input terminals for proper connection.

Input power can be from 11 to 28 Vdc and will draw less than 2 watts.

If properly connected, the front panel Green LED will be illuminated. Before

reapplying power, visually inspect the power supply and the input power

connections for any discrepancy which could have caused the overload.

(b)

If the transducer has some preloading, the BALANCE controls may not

allow successful zeroing of the instrument output. This condition can be

remedied by connecting a resistor (50 k- 200 k range, metal-film type)

from the +Signal terminal of the transducer to the + or – Excitation Sense

terminals. The Excitation terminal to which the connection is made is

determined by the direction of the loading or off-zero reading.

(c)

The inability to balance correctly, where the instrument output reads

totally off scale and the BALANCE controls have no authority, can very

likely be the result of a damaged or defective transducer or cable. This

possibility can be confirmed (or eliminated) by substituting a transducer

and cable known to be in good condition or by simulating a balanced

transducer, using either a commercially available transducer simulator

or the simple star bridge arrangement shown in Figure 7. The star bridge

simulates a conventional four-arm bridge in an exact condition of bal-

ance. To construct a star bridge, connect four 10% carbon resistors as

shown in Figure 5. Use 180-ohm resistors to simulate a 350-ohm bridge

and use 56-ohm resistors to simulate a 120-ohm bridge. Neither the

resistor values nor temperature characteristics are critical since the

balance condition of a star bridge is not determined by the resistance

values. Solder two resistors together, then solder the remaining two

resistors together. Next, connect the two junctions together using a

separate wire as shown. There is a good reason for this method of

construction, and it should be followed. Connect the substitute or simu-

lated transducer to the instrument I/O connector using a short 4-wire

cable configuration as shown in Figure 4. Attempt to balance the substitute

simulated transducer. If conditions now appear to be normal, the transducer

or cable is at fault. If the previous difficulties persist, the 5M78 is faulty.