Measurement Modes: Hardware Clock

Measurement Modes: Hardware Clock

In the Hardware clock measurement mode, timers create the clock on the devices. Use the Hardware clock to acquire data at high sampling rates. The maximum clock rate depends on the hardware used and almost always reaches the specified maximum sampling rate of the device.

You can use the hardware clock only with analog inputs that can read values to a buffer, controlled by a timer. The hardware clock does not process digital values.

The hardware clock achieves very high sampling rates. DIAdem transfers the rate you want and the channel list, to the board and starts the measurement. The hardware acquires the data independently and collects the data. The computer only forwards and processes data.

The measured data first goes into the measurement hardware buffer. The data is read from this buffer at regular intervals and forwarded to DIAdem. Data output has priority because the device buffer is limited. DIAdem buffers the data again if the data is not processed immediately. This computer buffer can expand to several megabytes for very fast measurements.

The Hardware clock delivers data that is acquired at a guaranteed high-speed rate. However, processing is always slightly delayed, because the data can never be read from the buffer in real time. In many applications, it is irrelevant whether data is displayed or saved a few milliseconds slower, as long as the end-result and the time reference are correct. However, if immediate reactions are required during the measurement, the delay can lead to unacceptable results.

Because digital signals cannot be recorded in the Hardware clock, the signals must be measured parallel in Software clocks. This can lead to delays, because the timers on the computer and the measurement device cannot be synchronized at the start of or during the measurement. Because two timers never start at exactly the same time and never run at exactly the same speed, the times in the time channels are not exactly the same after a measurement. The deviation usually amounts to a few milliseconds.

If you want the hardware clock measurement to run in an external clock, you must connect the clock signal on all the NI boards in the measurement to the PFI1 terminal. Measurements that run with external clocks have no timeout monitoring in the driver, so data can also be acquired when the machines are running.

If you use a DAQ board that cannot use a PFI1 terminal as the external clock input, earlier DIAdem versions did not allow you to use this board with an external clock. For this board type, DIAdem 9.0 and later versions use the STARTSCAN signal as the external clock input. For these DAQ boards, you must connect the external clock signal to the STARTSCAN terminal, not to the PFI1 terminal. If the DAQ board does not support this, DIAdem terminates the measurement preparations with an error message. Refer to the hardware documentation for information about the terminal assignment on the hardware.