Honeywell Chadwick-Helmuth 8500C Maintenance Manual page 171

Procedure
1. With nothing connected to the input of the Charge Fixture, connect its output the 8520CS input.
2. Measure the 8520CS input capacitance (between TP1 and TP2 of the Charge Fixture). Record this
value as C (pF) (should be about 0.1 mfd = 100,000 pF).
in
3. Determine the capacitance and charge sensitivity of the intended acclerometer:C
S (pC/g).
Q
N O T E : S e n s o r
6 2 3 3 C - 5 0
7 7 0 4 A - 5 0
4. Connect the input of the Charge Fixture to a signal generator. Configure the generator for a 100
+0.1 Hz sinewave. Using a floating DVM, monitor the voltage between TP1 and TP2. Adjust the
generator for a DVM reading of 100 +0.1 mV
5. Connect the 8520CS according to Figure D-8.
6. Remove the cover from the 8520CS and set the DIP switch for the charge sensitivity closest to that
of the intended accelerometer. This switch is set according to the Decal inside the instrumenct. See
Table D-4 for channel switch and potentiometer adjustments. See Figure D-10 for DIP switch
settings. See Figure D-9 for potentiometer and DIP switch locations on the Signal Conditioner PC
board.
7. Calculate the required 8500C/C+ ips reading:
(
i p s = V 2
8 5 0 0 C i n
W h e r e : V :
i n
C :
i n
C :
a u
f :
S Q :
8. Set up the 8500C/C+ for BALANCE. In SETUP set the balance frequency to 100 hz, and the
balance type to STROBEX. Also select MANUAL STOP.
9. Press ENTER softkey, wait 10 seconds, then press START and adjust the 8520CS trimpot (see
Table D-4) for an 8500C/C+ reading of the value calculated in step 7. Ignore the STROBEX
instructions; press STOP when finished.
EXAMPLE: You wish to calibrate and 8520CS which is intended to be used with an
Endevco 6233C-50 accelerometer connected to 8520CS.
You've measured the input capacitance of the 8520CS: C
You've set the generator for: V
Assume the 6233C-50 accelerometer has:
SQ = 50 pC/g, C
acc
Hence,
(
i p s = 0 . 1 0 0 2
8 5 0 0 C
C ( p . )
a c c
1 3 5 0
2 8 0 0
)
6 1 . 4 5 ( C + C )
i n a c c
f S
Q
= 100 mV between TP1 and TP2 (f = 100 hz sine wave).
in rms
= 1350 pF.
6 1 . 4 5 ( 1 0 0 4 0 0 + 1 3 5 0 )
1 0 0 5 0
Calibration - Charge Converter Amplifiers
S ( p C / g )
Q
5 0
5 0 ( N o m i n a l )
.
rms
= 100400 pF.
in
)
= 1 7 6 . 8 i p s ( p K ) + 1 %
8500C/8500C+ System Maintenance Manual D-13
(pF) and
aac