Multichannel Systems nanoZ manual - Manual (Page 30)

nanoZ User Manual
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Arguments: handle – handle to an opened device returned by the open function;
nsam_measure – number of samples to measure per single impedance reading;
numdsps – number of overlapping impedance measurements.
Return values: none.
Remarks: Calling this function initiates the impedance measurement process,
applying sinusoidal test current to the target electrode and measuring the voltage
across it. After a given number of samples is collected (which is specified by the
nsam_measure argument), the data are converted to a single, average impedance
reading. Because it may take considerable time, typically about a second, to
collect data for result conversion, it is possible to perform multiple concurrent
conversions, partially overlapping in time with each other. This allows more
impedance readings per second. The multiplication factor is specified as the
numdsps parameter. For example, if one measurement lasts one second, and
numdsps parameter is set to 4, there will be 4 impedance readings per second.
While measuring impedance, the user program has to poll the results by calling
the getimpdata function every ~30ms, or a data buffer overrun may occur.
Prior to measuring impedance, a channel must be selected and a working
frequency must be specified by calling the selectchannel and setfreq functions,
respectively.
getimpdata
Retrieves impedance measurement data.
Usage: [signal_samples, Z] = nanoz(‘getimpdata’, handle);
Arguments: handle – handle to an opened device returned by the open function.
Return values: signal_samples – vector of integers which are raw analog signal
readings from the target electrode. The user application may use these readings
in order to monitor, for example, the noise and interference levels during
impedance measurement. If the signal is not clean, the impedance reading may
be inaccurate.
Z – vector of complex impedance readings, in Ohms.
Remarks: During impedance measurement, the user program must call this
function approximately every 30ms to poll for incoming data. Output vectors are
sized according to the amount of new data that were collected between two
successive calls of this function. If no data were acquired, the vectors will be
empty. In typical situations, the Z vector is empty most of the time, but
occasionally it has one element – the impedance reading that was most recently
acquired.