MF Threshold Unit
Zurich Instruments offers a unit for state detection with hardware triggers and associated logical operations on lock-in amplifier and PID controller measurements. The MF Threshold Unit is included with every MFLI Lock-in Amplifier and MFIA Impedance Analyzer; additional upgrades such as the MF-PID Quad PID/PLL Controller and the MF-MD Multi-Demodulator options extend an instrument's functionalities even further.
The Threshold Unit performs logical analysis on measurement data in real time. Starting from the analog or logical measurement data, users can define multiple operations to detect specific conditions and trigger a reaction via a TTL output.
- 4 threshold units
- Analog input parameters: demodulator samples (X, Y, R, Θ), PID error, PID output value, PID shift (requires MF-PID option)
- Absolute-value and low-pass filtering applicable prior to threshold detection
- Threshold detection: above, below, outside, inside, rising edge, falling edge
- Configurable activation and deactivation times
- Digital input signals: 32 DIO channels, input and output overflows, etc.
- Combination of up to 3 logical signals with NOT, AND, OR, and XOR operations
- Minimum length, hold and invert functionality
A dedicated tab in LabOne accommodates the 4 threshold units, represented as 4 rows (see figure). Each row is divided into a Thresholds section to the left and a Logicals section to the right.
The Thresholds section turns analog signals into logical signals. Applying an adjustable first-order low-pass filter to the measurement data or their absolute values makes signals smoother and avoids false alarms when small glitches occur. The resulting filtered threshold signal can then be displayed in the Scope. Based on the filtered threshold signal, users can define one or two threshold levels to determine a logical signal corresponding to the conditions above, below, outside, rising edge, and falling edge. Individual activation and deactivation times can be set to ensure that the logical signal timing and reliability meet every user's requirements.
When logical signals are selected as inputs of the Thresholds section, the activation and deactivation times can be set in the same way as for the analog signals. The following logical signals are available: 32 DIO channels, 2 trigger inputs, 2 trigger outputs, Input Overflow (I), Input Overflow (V), Output Overflow, Aux Input Overflow, Aux Output Overflow, 4 PID output overflows.
In the Logicals section, it is possible to combine up to 3 logical signals from the Thresholds section and other sources using NOT, AND, OR, and XOR operations. This means that feedback conditions can be tailored to meet complex patterns based on multiple analog and digital signal sources. Setting the minimum signal length ensures that no event will be missed, even if the rest of the hardware cannot detect very short events. Every logical signal can also be inverted before the output.
Each of the 4 logical signals generated by the Threshold Unit can be assigned to one of the 32 DIO channels (SCSI connector on the back panel) or to either of the 2 trigger outputs.
In addition to the logical signals, each Threshold Unit generates a filtered threshold signal used for state detection and triggering. These signals can be output through one of the 4 auxiliary outputs with the offsets, scaling, and limit features. Moreover, the signals are available as trigger sources and display signals in the Scope.
Examples of Applications
Microfluidic impedance spectroscopy and cell sorting
One application of impedance spectroscopy on microfluidic channels is the characterization of individual biological cells. The Threshold Unit allows users to go one step further: with the right set of parameters in place, cells with different properties can be reliably sorted into different containers.
AFM tip protection
Many atomic force microscopy (AFM) modes are supported by the MFLI Lock-in Amplifier. In combination with the MF-PID Quad PID/PLL Controller option, the MF-MD Multi-Demodulator option, and the MF-MOD Modulation option, the following AFM-related functionality is available:
- Automatic gain control (AGC)
- Frequency modulation (FM)
- Kelvin-probe-force microscopy (FM-KPFM, AM-KPFM)
- STS IETS
- Multi-frequency AFM
- Sideband analysis
The Threshold Unit helps to increase the tip lifetime thanks to a feedback mechanism that quickly increases the distance between the tip/probe and the surface to avoid damage. The sensing of critical situations can be based on various signals, e.g. the PID error of the frequency modulation control loop or the PID output value of the automatic gain control loop.