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Glossary92

8 Glossary

AC/DC switch. To switch from AC coupling to DC coupling, or vice versa, select AC or

DC from the control on the PicoScope toolbar. The AC setting filters out very low-

frequency components of the input signal, including DC, and is suitable for viewing

small AC signals superimposed on a DC or slowly changing offset. In this mode you

can measure the peak-to-peak amplitude of an AC signal but not its absolute value.

Use the DC setting for measuring the absolute value of a signal.

ADC. Analog-to-digital converter. The electronic component in a PC oscilloscope that

converts analog signals from the inputs into digital data suitable for transmission to

the PC.

Block mode. A sampling mode in which the computer prompts the oscilloscope to

collect a block of data into its internal memory before stopping the oscilloscope and

transferring the whole block into computer memory. Choose this mode of operation

when the input signal being sampled contains high frequencies. Note: To avoid

sampling errors, the maximum input frequency must be less than half the sampling

rate.

Buffer size. The size of the oscilloscope buffer memory, measured in samples. The

buffer allows the oscilloscope to sample data faster than it can transfer it to the

computer.

Callback. A mechanism that the PicoScope 4000 driver uses to communicate

asynchronously with your application. At design time, you add a function (a callback

function) to your application to deal with captured data. At run time, when you request

captured data from the driver, you also pass it a pointer to your function. The driver

then returns control to your application, allowing it to perform other tasks until the

data is ready. When this happens, the driver calls your function in a new thread to

signal that the data is ready. It is then up to your function to communicate this fact to

the rest of your application.

Device Manager. Device Manager is a Windows program that displays the current

hardware configuration of your computer. On Windows XP or Vista, right-click 'My

Computer,' choose 'Properties', then click the 'Hardware' tab and the 'Device Manager'

button.

Driver. A program that controls a piece of hardware. The driver for the PicoScope

4000 Series PC Oscilloscopes is supplied in the form of a 32-bit Windows DLL,

ps4000.dll. This is used by the PicoScope software, and by user-designed

applications, to control the oscilloscopes.

ETS. Equivalent-time sampling. A technique for increasing the effective sampling rate

of an oscilloscope beyond the maximum sampling rate of its ADC. The scope triggers

on successive cycles of a repetitive waveform and collects one sample from each cycle.

Each sample is delayed relative to the trigger by a time that increases with each cycle,

so that after a number of cycles a complete period of the waveform has been sampled.

The waveform must be stable and repetitive for this method to work.

GS/s. Gigasample (billion samples) per second.

Maximum sampling rate. A figure indicating the maximum number of samples the

oscilloscope can acquire per second. The higher the sampling rate of the oscilloscope,

the more accurate the representation of the high-frequency details in a fast signal.

MS/s. Megasample (million samples) per second.