About analog to digital converter (ADC) functionality
- Gisela Roberts
- Ben Stanley
To capture data from third-party devices, such as force plates and electromyography (EMG) equipment, to a Vicon system, your Vicon system must include a Vicon Lock unit, which provides analog to digital converter (ADC) functionality.
Vicon Lock Lab supports up to 64 analog channels. You can extend the number of analog channels in your Vicon system by adding a further Lock.
The ADC captures up to 64 separate inputs for generating 16-bit offset binary conversions from the analog sources. The input impedance is 1 MΩ (ohm). The data sampling frequency is common to all channels; you can set the sampling rate to be a multiple of the camera base rate up to 192,000 samples/second (192 KHz). The capture frequency you can specify depends on the total number of channels to be sampled, as shown in the following table.
| No. of channels available | Max. capture frequency (KHz) | Allocated channel input no. |
|---|---|---|
| 64 | 3 | 1–64 |
| 32 | 6 | 1–32 |
| 16 | 12 | 1–16 |
| 8 | 24 | 1–8 |
| 4 | 48 | 1–4 |
| 2 | 96 | 1–2 |
| 1 | 192 | 1 |
As the table shows, increasing the sample rate above 3 KHz automatically reduces the number of channels available for capturing. Irrespective of the sampling rate selected, there is always a fixed 5.2uS timing offset (one period of 192KHz) between physically adjacent channels.
When sampling at capture frequencies greater than 3KHz, the upper channels can no longer be sampled, so the remaining channels to be sampled must be justified to the first channel positions (that is, they must begin at the first channel).
Each channel has a programmable gain, which can be set to +/-10 volts, +/-5 volts, +/-2.5 volts, or +/-1.25 volts. This gain (or attenuation) automatically scales the input signal to the dynamic range of the ADC sampling device (which is +/- 2.5 volts) thus guaranteeing the best signal-to-noise ratio. For details on specifying these settings, see your Vicon software documentation.
