Measurement Specialties CIO-SSH16 Adding Amplifiers Sample / Hold Chips, Range Calculation

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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