Omega OMB-DAQBOARD-3000 사용자 설명서
1-6 Daq Systems and Device Overviews
988093
DaqBoard/3000 Series User’s Manual
Example 2: Analog channel scanning of voltage and temperature inputs
The figure below shows a more complicated acquisition. The scan is programmed pre-acquisition and is
made up of 6 analog channels (Ch0, Ch2, Ch5, Ch11, Ch22, Ch23.) Each of these analog channels can
have a different gain. Two of the channels (22 and 23) are from a PDQ30 expansion module. These two
channels can be programmed to directly measure thermocouples. In this mode, oversampling is
programmable up to 256 oversamples per channel in the scan group. When oversampling is applied, it is
applied to all analog channels in the scan group, including temperature and voltage channels. (Digital
channels are not oversampled.) If the desired number of oversamples is 256 then each analog channel in
the scan group will take 256 microseconds, the returned 16-bit value represents an average of 256
consecutive 1us samples of that channel. The acquisition is triggered and 16-bit values (each representing
an average of 256) stream to the PC via DMA.
Since two of the channels in the scan group are temperature channels, the acquisition engine will be
required to read a cold-junction-compensation (CJC) temperature every scan. In fact, depending upon
which PDQ30 channels are being used for temperature, there may be a CJC temperature required for each
temperature channel in the scan. Each 4 channel terminal block of the PDQ30 shares one CJC so if all
temperature channels are grouped on one (of the six) terminal blocks, then only one CJC temperature
measurement will need to be made per scan. For every PDQ30 terminal block that is measuring at least
one temperature channel, one additional CJC temperature measurement will be automatically added to the
scan group. This increases the scan period and reduces the maximum scanning frequency.
made up of 6 analog channels (Ch0, Ch2, Ch5, Ch11, Ch22, Ch23.) Each of these analog channels can
have a different gain. Two of the channels (22 and 23) are from a PDQ30 expansion module. These two
channels can be programmed to directly measure thermocouples. In this mode, oversampling is
programmable up to 256 oversamples per channel in the scan group. When oversampling is applied, it is
applied to all analog channels in the scan group, including temperature and voltage channels. (Digital
channels are not oversampled.) If the desired number of oversamples is 256 then each analog channel in
the scan group will take 256 microseconds, the returned 16-bit value represents an average of 256
consecutive 1us samples of that channel. The acquisition is triggered and 16-bit values (each representing
an average of 256) stream to the PC via DMA.
Since two of the channels in the scan group are temperature channels, the acquisition engine will be
required to read a cold-junction-compensation (CJC) temperature every scan. In fact, depending upon
which PDQ30 channels are being used for temperature, there may be a CJC temperature required for each
temperature channel in the scan. Each 4 channel terminal block of the PDQ30 shares one CJC so if all
temperature channels are grouped on one (of the six) terminal blocks, then only one CJC temperature
measurement will need to be made per scan. For every PDQ30 terminal block that is measuring at least
one temperature channel, one additional CJC temperature measurement will be automatically added to the
scan group. This increases the scan period and reduces the maximum scanning frequency.
In this example, the desired number of oversamples is 256, therefore each analog channel in the scan group
requires 256 microseconds to return one 16-bit value. The oversampling is also done for CJC temperature
measurement channels. The minimum required scan period for this example is therefore 7 X 256 us or
1792 microseconds. The maximum scan frequency is the inverse of this number, 558 Hz.
requires 256 microseconds to return one 16-bit value. The oversampling is also done for CJC temperature
measurement channels. The minimum required scan period for this example is therefore 7 X 256 us or
1792 microseconds. The maximum scan frequency is the inverse of this number, 558 Hz.
Autozero may also be employed. This adds more channels to the scan group and further reduces the
maximum scan frequency. Auto zero channels read a shorted analog input that is internal to the PDQ30.
Auto zeroing reduces drift due to fluctuating ambient temperatures or ambient temperatures outside the DC
specifications.
maximum scan frequency. Auto zero channels read a shorted analog input that is internal to the PDQ30.
Auto zeroing reduces drift due to fluctuating ambient temperatures or ambient temperatures outside the DC
specifications.