LCRmeter
Usage
Sweep mode vs. Step mode
The LCRmeter provides two modes to vary and apply parameters. The Sweep mode is similar to the Sweep mode that can be found in many other modules. For a capacitance-voltage (CV) curve one would use "Voltage" as Sweep mode while a capacitance-frequency (Cf) curve is obtained by using "Frequency" as Sweep mode. The Sweep values that are successively applied to the sample are typically created via the Sweep editor that comes with LCRmeter module.
The Step mode, depending on the Device Class, can be used to create a further parameter variation. For example, capacitance-frequency curves are often measured at different bias voltage. Thus, one would change Step mode to "Voltage". The Step values, however, cannot be created by the internal Sweep editor of the LCRmeter module. For that reason, one can add a module named 'Sweep' to the sequencer just one level higher than the LCRmeter module. Now, the values defined in that module can be handed over to the LCRmeter module by selecting "Sweep value of <label of the module>" as source for the Step value. Why is that so? By having different origins for the values for Sweep value and Step value, one can create sequencer procedure where MakeFile is embedded such a way that a new file is created for each step, but not for each sweep.
Device class programming
Specialties
Each Device Class for the LCRmeter module must return the first three variables as following:
- "R" the real part of the impedance R,
- "X" the imaginary part of the impedance X, and
- "Frequency", the frequency
If this is the case, the Device Class is accepted.
Post-processing
The module can automatically calculate several important values based on R, X, and f. Whenever a Device Class returns those values as the first three variables, the post processing can be use. Then, all selected values are calculated appended to the variables that are returned by the Device Class.
Please note that you can always check the correct calculation by doing it on your own to scientifically verify the results, e.g. by using a Calc module.
The LCRmeter module automatically calculates the capacitance, absolute impedance (modulus), and phase, and appends it to the measured values. The formulas used are as given below. Please note that you always can check the correct calculation by doing it on your own to scientifically verify the results.
Basic values
These values can be calculated independent from any circuit or other assumptions.
Modulus Z in V/A
|Z| = (R**2 + X**2)**0.5
Angle in degree
Phi = math.atan(X/R)/math.pi*180.0
Angle in rad
Phi = math.atan(X/R)
Angular frequency in 1/s
w = 2 * math.pi * f
Parallel circuit
These values can be calculated by assuming that a capacitor with Cp and a resistor with Rp are connected in parallel. In case of an inductor with Lp, it is a parallel connection of Lp and Rp.
Parallel capacitance Cp in F
Cp = -X/2.0/math.pi/f/|Z|**2
Parallel resistance Rp in V/A
Rp = R * (1 + (X/R)**2)
Parallel conductance Gp in V/A
Gp = 1 / Rp
Parallel inductance Lp in V/A
Lp = X / 2 / math.pi / f * ( 1.0 + 1.0 / (X/R)**2 )
Series circuit
These values can be calculated by assuming that a capacitor with Cs and a resistor with Rs are connected in series. In case of an inductor with Ls, it is a series connection of Ls and Rs.
Series capacitance Cs in F
Cs = -1/2.0/math.pi/f/X
Series resistance Rs in V/A
Rs = R
Parallel conductance Gp in V/A
Gs = 1 / Rs
Series inductance Ls in H
Ls = X / 2.0 / math.pi / f
These values are calculated for reasons of convenience. We would like to emphasize that the extraction of resistances, capacitances and inductances always rely on the assumption of a particular circuit. In many cases, a simple parallel or series circuit is not adequate to understande the bias or frequency dependent characteristic of the impedance. In such a case, the impedance must be evaluated and fitted by extended equivalent circuits.
The formulas presented above can be seen in the Table 1 that can be found here: http://www.phys.ufl.edu/~majewski/nqr/paper/nqr_detection_educational/series-parallel-impedance-parameters-an.pdf
Supported parameters
There are string-type keys that can be used during Device Class programming to interact with the GUI of the LCRmeter module which are listed here.
SweepMode
A ComboBox with the currently selected Sweep mode.
StepMode
A ComboBox with the currently selected Step mode.
ValueTypeRMS
A ComboBox that can be used to define different options for the AC signal. For example, most LCRmeter can apply either a current or a voltage signal. If there is only possible
ValueRMS
A LineEdit with the value of the selected type in ValueTypeRMS.
ALC
A ComboBox to present different modes for Automatic Level Control (ALC). ALC makes sure that the correct signal is applied to the device under test. Caution: If one of the measurement ports is not correctly connected to the device, the LCRmeter might apply higher voltages than desired.
OperatingMode
A ComboBox to provide the measurement mode, e.g. 'R-X', 'Cp-D', 'Cp-Gp', or 'Ls-Rs'. The definition of these opions relies on the Device Class. We recommend to keep the format '<variable1>-<variable2>' and use 'p' or 's' to indicate whether the values have been derived by assuming either a parallel or a series circuit, respectively.
Integration
A ComboBox to provide different integration modi.
Average
A ComboBox to provide different average modi or a number of averages.
Range
A ComboBox to provide different current measurement ranges. Default first option should be "Auto" if the instrument supports it.
Trigger
A ComboBox to choose the source of the trigger signal.
TriggerDelay
A LineEdit to enter the delay at which the measurement starts after the trigger signal arrives.