3.3. Basic Measurement Operation

To configure a measure module on the front panel, navigate to the tab for the module. Note that additional settings as applicable to a specific module will also be displayed here. For information on those settings, see Modules.

This first setting is the mode setting. The mode setting will determine what type of processing (DC, AC, or Lock-in) is performed by the M81-SSM on the signal received from the module. The other settings displayed will change based on what is relevant in the selected mode.

To change the mode on the front panel, tap the mode and select a new mode.
Interface Command: SENSe#:MODE

DC Mode

../_images/dc_basic_settings.png

Figure 3.9 DC mode

Display

In DC mode, the display can be configured to show either the DC measurement, Relative DC measurement, or calculated resistance. Tap the three dots or the resistance symbol in the upper right hand corner of the display area to change which value is displayed. When displaying the Relative DC measurement, the ZERO/CLEAR button can be used to modify the baseline for the relative measurement. For more information on the calculated resistance, see Calculated Resistance. For more information on the Relative DC measurement, see Relative Measurement.

Averaging Time

The averaging time is specified in number of power line cycles (NPLC). Note that the MeasureReady™ M81-SSM detects the power line frequency in your country. For example, if your power line frequency is 60 Hz, setting an NPLC averaging time of 30 NPLCs would mean an averaging time of 0.5 s. For best rejection of line-related interference, an integer number of NPLC should be selected.

Interface Command: SENSe#:NPLCycles

AC Mode

../_images/ac_basic_settings.png

Figure 3.10 AC mode

Display

In AC mode, the display can be configured to show either total RMS and DC measurements, relative RMS measurement, or +Peak, -Peak, and Peak to Peak measurements. Tap the three dots in the upper right hand corner of the display area to change what is displayed. When displaying the Relative RMS measurement, the ZERO/CLEAR button can be used to modify the baseline for the relative measurement. For more information on the Relative RMS measurement, see Relative Measurement.

  • Total RMS The total power of the input signal, including AC and DC components within the observation window

  • DC The DC level of the input signal

  • +Peak The highest input level detected during the observation window

  • -Peak The lowest input level detected during the observation window

  • Peak to Peak The span between the highest and lowest input levels detected during the observation window

Observation Time

The observation time is specified in number of power line cycles (NPLC). Note that the M81-SSM detects the power line frequency in your country. For example, if your power line frequency is 60 Hz, setting an averaging time of 30 NPLC would mean an averaging time of 0.5 s. For best rejection of line-related interference, an integer number of NPLC should be selected.

Interface Command: SENSe#:NPLCycles

Lock-In Mode

In lock-in mode, the M81-SSM will detect signals that are coherent with the configured reference signal. For more information about the underlying concepts of lock-in operation, see section Lock-In Amplifier Background.

../_images/lia_display.png

Figure 3.11 Lock-in mode display

../_images/lia_basic_settings.png

Figure 3.12 Lock-in mode settings

Display

In lock-in mode, the display can be configured to show either rectangular coordinates (\(X\), \(Y\)), polar coordinates (\(R\), \(θ\)), or the calculated resistance. In addition, the percent of range and frequency are always displayed. Tap the three dots or the resistance symbol in the upper right hand corner of the display area to change what is displayed. For more information on the calculated resistance, see Calculated Resistance.

  • X The real (in-phase) component of the detected signal

  • Y The imaginary (quadrature) component of the detected signal

  • R The magnitude of the detected signal

  • θ The phase of the detected signal relative to the reference signal

  • % of Range The amount of the present range being used by the total input signal, including any noise

  • Frequency The frequency of the reference signal

Reference Source

The measure channel will detect frequencies which are coherent with the specified reference source. For example, if a sample is being excited with a current by S1, the reference source can be set to S1. The reference source can also be set to Ref In. In this case the source will track the frequency detected on the reference input.

When reference source is set to a source channel, two additional read-only settings will appear. These settings display the amplitude and offset for the specified source module. However, the below states maybe shown.

  • Disconnected The selected source channel does not have a source module connected.

  • Unloaded The selected source channel has a source module connected, but the source module is not loaded.

  • Module error The selected source channel has an error on the module, which can be viewed by selecting the relevant source channel tab.

Interface Command: SENSe#:LIA:RSOurce

Reference Harmonic

The reference harmonic can be set to detect signals at a frequency that is a harmonic of the reference. For example, if the reference frequency is 1 kHz, setting reference harmonic to 2 would result in detecting signals at 2 kHz, which are coherent with the reference.

Interface Command: SENSe#:LIA:DHARmonic

Reference Phase Shift

The reference phase shift is applied to the reference source before using the reference for demodulation. Tap auto to set the phase shift to result in zero degrees of indicated angle. Note that the measurement should be settled before tapping auto. Tap clear to set the phase shift to zero.

Interface Command: SENSe#:LIA:DPHase

Time Constant

The time constant setting determines the bandwidth of the PSD output filter. Longer time constants will result in lower equivalent noise bandwidth (ENBW) at the cost of longer settle times. See table below.

Interface Command: SENSe#:LIA:TIMEconstant

Rolloff

The rolloff setting determines the slope of the PSD output filter in the stop band. Steeper rolloff will result in lower ENBW at the cost of longer settle times. Steeper rolloff will also provide better rejection of interfering signals that are near the frequency of interest.

Interface Command: SENSe#:LIA:ROLLoff

For time constant \(\tau\), the ENBW and time to settle can be seen in the choosing lock-in filter settings table.