Ectron 451, Instruction Manual

Page: 24 / 74

Scale Mode Exit By pressing the display at this screen, the user returns
to
SCALE MODE SETUP
.
AUTOZERO
Local Autozero
This main-menu selection is reached in two ways. If
zero is already on, it will be the first screen seen when
the display is pressed from the operate screens. When
zero is off, then it is reached by pressing the display
and rotating the encoder until the main-menu selection
AUTOZERO is displayed. When the display is pressed
from this screen, the user is asked to confirm an autozero
by answering
YES or NO . Whether YES or NO is
selected, the main-menu selection
AUTOZERO
is again
displayed. When the display is pressed when YES has
been selected, an autozero is attempted. (Also if
YES
is selected, zero offset will be turned on if previously
off.) If autozero is possible, the temporary screen
PLEASE WAIT is displayed, and autozero is performed.
If it is not (because the output exceeds the range of
autozero), the screen
ZERO OUT OF RANGE will
displayed.
The internal microprocessor knows what the output volt-
age is, so when an autozero is commanded, the output
is offset by that amount (up to
±
10 V dc). Autozero is
accomplished at the output of the Model 451; therefore,
even if autozero does zero the output, the user should
be aware that the usable (remaining) range of the input
may be severely limited. For example, if the input volt-
age is 0.9 V ac, and the gain is set to 10 (thus, a 9-V-dc
output), there is only 0.15 V (the voltage necessary to
reach the output limit of 10.5 V dc) of range remaining
for the input to operate in the positive direction, although
a valid autozero can be commanded forcing the output
to zero. This means that if the user now increases the
input to 1.1 V ac (0.2 V ac more than the original 0.9
V ac), the screen
INPUT OUT OF RANGE
will appear
even though one might expect the output to be 2 V dc
(9 V minus 9 V of autozero plus the 0.2 V input times
the gain of 10).
Remote Autozero
Autozero can be commanded remotely by connecting
Pin 5 of the connector to any voltage between 10.5 and
32 V dc with reference to Output Low, Pin 11. If the
user wishes to uses the same power supply as that which
powers the Model 451, Pin 11 and Pin 15 must be con-
nected together. When remote autozero is commanded
the display will read
A-ZERO PLEASE WAIT
or
ZERO OUT OF RANGE . Refer to the previous para-
graphs for a discussion of “zero out of range.”
Operation Model 451
3-8