4. VERIFICATION OF NORMAL OPERATION
It is the purpose of this section to aid the user in determining, in the event of a malfunction
of which the Model IL70A 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, perform the following steps.
(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)
Figure 7. Star Bridge Construction
20
The inability to balance correctly, where the instrument output readstotally 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 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 IL70A may be faulty.
DC Strain Gage Conditoner
Module
IL70A
