Chapter 4: A/D
This chapter will deal with the various A/D channels and manipulating the data obtained from them.
Sampling Rate
The A/D converter has a conversion time around 10 microseconds, however, the actual sampling rate is limited by the serial communications. The actual sampling rate for a single channel is around 120 samples per second (9600 baud). This rate drops to around 41 samples per second when sampling all of the channels. When reading an A/D input, the 232OPSDA takes four readings and returns the average (0.5 and greater are rounded up) of these readings. This averaging helps filter out noise.
A/D Converter Range
The actual A/D converter chip in the 232OPSDA is a 12 bit A/D converter that can read analog voltages between 0 and 5VDC. However, the 232OPSDA contains signal conditioning circuitry that allows you to measure voltages from 0 to 10VDC (Gain = 0.5) as well as other ranges. In the following sections, each channel configuration will be covered.
Non-buffered 0 to 5VDC A/D Inputs
The 232OPSDA has two
Buffered 0 to 5V A/D Inputs
The 232OPSDA has two buffered 0 to 5V inputs. They are A/D 1 on Terminal Block 1 and A/D 2 on Terminal Block 2. An operational amplifier is setup as a voltage follower to buffer the A/D converter from the source of the voltage. The input resistance of each of these channels is 1TΩ . This allows you to have a large source impedance.
Both A/D 1 and A/D 2 are set up as voltage followers with a gain of 1 when they leave the factory. However, the voltage follower for A/D 1 (TB 1) has spaces for optional through hole resistors. This allows you to reconfigure A/D 1 into a
1.See the circuit schematic in Figure B.1 and board layout in Figure B.2 in Appendix B. To change the voltage follower into a non-
Documentation Number 232OPSDA1397 Manual | 15 |
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