DayTronic IL78A Handbuch - Seite 14

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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 IL78A 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.

f the unit is totally inoperational (front-panel power indicator does not light),

(a)

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.

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

(b)

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.

The inability to balance correctly, where the instrument output readstotally off scale

(c)

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

balance. 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 simulated 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 IL78A is faulty.

AC Strain Gage Conditioner Module

Verification of Operation IL78A.3

IL78A