Characteristics of A/D converters

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If the sampling time and conversion of short A/D converter in general is faster as its structure seems more complex and therefore more expensive. There are several performance converters that will work on similar principles, for example by the value of the analog signal will change capacity varicap diodes and will change the frequency generator that is used is used as an intermediate stage in the conversion. But these are details that will be the end result reflected in the accuracy and speed of measurement.

The following example shows the typical characteristics of the A/D converter.


Example II

Offer transducer manufacturers 'National Instruments' - U.S. for various computer bus.

PC AT / XT / EISA compatible cards with A/D converters
BUS AT AT AT AT XT/
AT
LPT EISA AT
Analog
inputs
8 32 8 8 4 4 4 2
Sampling
(kHz)
 500  333  100  100 83.33  100 1000 51.25
Resolution
(bits)
12 12 12 16 12 12 12 16
Measuring
range (V)
+,-10
+,-5
+,-10
+,-5
+,-10
+,-5
+,-10 +,-10 +,-10 +,-5 +,-2.8
Amplification
/areas
1÷100
/7
1÷100
/7
1÷100
/7
1÷100
/7
1÷100
/7
1÷100
/7
1 1
Analog
outputs
2 2 2 2 2 2 - 2
Resolution
(bits)
12 12 12 16 12 12 - 16
Digital
I/O channels
8 8 32 8 24 24 - -
Counters
2 2 2 3 3 3 - -
WINDOWS
support
yes yes yes yes yes yes yes yes
DOS
support
yes yes yes yes yes yes yes yes
Display
spectrum
no no no no no no no yes
Other
support
yes yes yes yes no no yes yes

Bright yellow color in the table refers to data that belong to the description of the analog inputs, the color blue relates to analog outputs and the green color refers to the program support that belongs to the devices. Labels of cards are not listed because they are not of importance for example. The above examples are just to indicate which parameters need to watch. Transducer performance with PCI, PCI-E or USB interface to the PC is just basically changed the way of communication with the computer and in most cases these are the same or improved transducer assemblies.

The number of analog input channels refers to the differential inputs (+,0,-), and their number is doubled when used separately (+,0 and 0,-). For examples see that are commonly prepared converters of 12 bit resolution which provides 4096 discrete values for sampling.

So, 16-bit converters are more accurate than 12-bit converters. If the test and expect little change of the observed values of the analog signal must be made when choosing to decide on the precise transducer or add special pre-amplifier for analog signal. Well when choosing to opt for components of the same manufacturer.

The table refers to standard offer manufacturers. As the transducers are not produced in huge quantities as other components of the computer price is rather large (about $ 1000 and up), especially if they are given to develop a peculiar purposes.

The interface converter is varied from case to case and is usually described in the manual that the transducer gain. The transducers are generally better and better software support and associated documentation, and when choosing a manufacturer needs to have these factors in mind.

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