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To calculate the effect of the droop rate on the accuracy of your measurement, the
range of the signal, the resolution of the A/D converter and the time between HOLD
and A/D acquisition are needed. Here is an example.
RANGE CALCULATION
Signal Range ±50 millivolts
Gain 100
Amplifier Output ±5 Volts At full scale
RESOLUTION CALCULATION
A/D resolution 12 bits 1 part in 4096
Volts per bit 2.44 millivolts 10/4096
TIME TO SAMPLE CALCULATION
Number of channels 8
Sample Rate 4,000 samples/ sec.
Time between samples 250 microseconds 1/4000
Time from HOLD to CH8 2 milliseconds 0.000250 * 8
DROOP CALCULATION
Maximum droop to CH8 ±0.0001V * 2 = ±2 microvolts.
Less than 8% of the value of 1 bit.
It is clear from this calculation that droop rate is not a problem even at low sampling
rates. The sample rate would have to drop to less than 400 samples/ sec. over eight
channels before the droop was detectable by a 12 bit A/D converter.
4.6 ADDING AMPLIFIERS &
SAMPLE / HOLD CHIPS
The CIO-SSH16 comes standard with
four amplifiers and three sample & hold
chips installed.
To add an additional channel, order the
two chip set, CIO-SSH-AMP shown
here. Twelve CIO-SSH-AMP chip sets
may be added for a total of 16 channels
(Figure 4-8). You can acquire LF398
S&H and INA110 amps on your own
and install them if you wish without
voiding your warranty.
Figure 4-8. CIO-SSH-AMP Chip Set
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