| There are two adjustments
in the FT-100 to calibrate the analog reference
voltages. One calibration sets the reference
voltage for the Analog Output circuitry (D/A),
and the other sets the reference voltage for the
Analog Input circuitry (A/D). Under normal
circumstances, these reference voltages should
not need adjustment; however, if service has been
performed on the FT-100 analog circuits or
routine calibration is required, this procedure
should be all that is needed.
The only equipment
needed for the voltage reference calibration is a
high quality and accurate voltmeter (digital
preferred). It is very important that the
calibration of the voltmeter be correct since the
FT-100 analog circuitry can be no more accurate
than the voltmeter used for calibration.
Calibrating
the A/D Reference Voltage
1. Unplug the
FT-100 unit and remove the cover (8 screws).
After the cover is removed,
reconnect AC power and turn on
the unit. Be very careful. There are dangerous
voltages
inside the unit!
2.
Connect the negative voltmeter lead to one of the
ground lines in the 40 pin I/O Interface
(front panel, center
connector).
3.
Connect the positive lead to the AA1 analog
output line (pin 5 of the 40 pin connector).
4.
The output voltage at AA1 will need to be set to
several voltages. This may be done through
Direct Commands, or the
following program may be loaded and run to
simplify the process:
REF_SET
;Program name
'
L1: AA1 = 0
LŲ: CLS
DISP "V Out = ";AA1
DISP "V In = ";AA9
WAIT
IF AA1 >= 10 THEN GOTO L1
AA1 = AA1 + 1: GOTO LŲ
/
This
program will set analog output AA1 and display
the voltage on the LCD. It also displays the
voltage at analog input AA9. Each time the WAIT
key is pressed, the output voltage at AA1 is
increased by 1.0 volt. After 10 volts, the output
is reset back to 0.0 volts. This program provides
a simple way of changing the output voltage, but
the same job may be done through Direct Commands.
5.
Set the analog output voltage to 2.0 volts
(either using the above program or through a
Direct
Command).
6.
Using a small screwdriver or tuning tool, adjust
the trimmer pot R58 until the voltage output is
equal to 2.0 volts.
7.
Now set the output voltage to 8.0 volts. Find the
median voltage between the actual output
voltage reading and 8.0 volts
and readjust R58 for this value. (Use the
following formula:
Median voltage = (8.0 + Actual
voltage) / 2)
8.
Check all the voltage readings, at 1.0 volt
increments, from 0.0 to 10.0 volts. The
conversion
from a digital number to an
analog voltage is done in steps of about 39.1 mv.
each. Each
individual output voltage may
not exactly equal the desired value, but should
be within the 39.1
mv. step. If any of the
readings are "off" by more than 39.1
mv., readjust R58 and check all
voltages again.
9.
This completes the analog output reference
adjustment. Now proceed to the analog input
reference adjustment.
Calibrating
the D/A Reference Voltage
NOTE:
It is very important that the analog output
reference be properly calibrated before
attempting to calibrate the analog input
reference!
1.
Connect the analog voltage output line AA1 to
analog input line AA9. Use either a jumper wire
or clip lead.
2.
Set the output voltage to 6.0 volts and adjust
trimmer pot R59 until V In = 6.0. (The analog
output voltage may be set by
using the above program or through Direct
Commands.
4.
Check all the voltage readings, at 1.0 volt
increments, from 0.0 to 10.0 volts, and readjust
R59
if necessary. The voltage
input and output readings should be the same.
Note: Even though
the analog conversion is done
in 39.1 mv. steps, these two readings should be
exactly equal
since the steps are the same
for input and output.
5.
This completes the analog reference voltage
adjustments. Unplug the FT-100 from AC power
and replace the cover.
NOTICE: Every effort has
been made to insure the accuracy of the
information contained in this document, however
Y-tek is not responsible for any consequences
resulting from erroneous or inaccurate
information.
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