SSH

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 Specifications

SSHXX

 Order Codes

Simulatenous Sample & Hold

Provide simultaneous sample and hold (S&H) between external signal conditioning and A/D card(s). These units can be used to ensure that all channels on A/D cards are sampled at the same time or ensure that all channels where multiple A/D cards are used, even in different PCs, are sampled at the same time.

Without S&H, the first channel will be sampled before the next and so on. For example; If all channels are driven by a sine wave at even a 1/10th of the sample rate each channel will record a significantly different value. Some A/D cards sample all channels in a burst, which reduces these problems of sample skew but increases potential channel cross-talk. Others spread out the channels throughout the sample to minimise cross-talk, resulting in maximum sample skew.

The S&H operates accepts a trigger pulse, from the A/D card or an external source. On receiving the pulse, S&H holds all current analogue input signal levels and then issues the trigger pulse to fire A/D conversion.

Apart from the obvious benefits, this signal conditioning also removes some of the pitfalls that afflict multiplexed multi-channels A/D cards. Some benefits are;

• Removes A/D sampling skew across single and multiple cards. With multiple cards, one card is designated the Master and issues the trigger pulse which it returned to it and all the other Slave A/D cards when the analogue signals are held.
• Reduction in sample rate is possible where increased sample rate has to be used to counter sample skew
• Low output impedance of the S&H can minimise or eliminate channel cross-talk by reducing the settling time for each channel within the A/D card after it is switched. This can be very bad where high source impedance and gain in the A/D card are used. Unused channels do not float, eliminating “cross-talk” inherited from adjacent channels.
• Provides a robust connection area for A/D card connections
• Protect the A/D card transient or overload damage. Even if damage occurs, the S&H will be easier to repair.