MF Threshold Unit

Zurich Instruments introduces the first functional 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 but of course, the functionality increases with further upgrades like the MF-PID Quad PID/PLL Controller option and the MF-MD multi-demodulator options installed.

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 can be applied 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.
  • combine up to 3 logical signals with NOT, AND, OR and XOR operations
  • minimum length, hold and invert functionality

The Threshold Unit performs logical analysis on measurement data in real time. Starting from the analog or logical measurement data the user can define multiple operations in order to detect specific conditions and trigger a reaction via a TTL output. 

LabOne Integration

A dedicated tab inside the LabOne user interface accommodates the four Threshold Units represented by four rows in the figure above. Each row is divided into a Threshold detection section on the left and the Logicals section on the right.

Thresholds section

The threshold section turns analog signals into logical signals. Measurement data or their absolute values can be subjected to an adjustable first order low pass filter that helps to smooth signals and avoid false alarms when small glitches occur. The resulting filtered threshold signal can be conveniently displayed in the LabOne Scope, for instance for bug fixing purposes. Based on the filtered threshold signal the user can then 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 the user's requirements.

When logical signals are selected as inputs of the threshold section, the activation and deactivation times can be set 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 Overflow.

Logicals section

In the Logicals section up to 3 logical signals from the threshold section and other sources can be combined using NOT, AND, OR and XOR operations. This means that feedback conditions can be tailored to meet even complex patterns based on multiple analog and digital signal sources. Setting the minimum signal length assures that no event will be missed even if the subsequent hardware is not capable of detecting very short events. Finally, every logical signal can be inverted before the output.

Signal availability

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 that is used for the state detection and triggering. These signals can be output via one of the 4 Auxiliary Outputs using the offsets, scaling and limit features there. Moreover, these signals are available as trigger sources and display signals in the scope.

Example 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 the user to go one step further and interpret the measurement information and to derive a feed forward to a splitting device. With the right set of parameters in place, cells of different properties can be reliably sorted into different containers.

AFM Tip Protection

There are many atomic force microscopy (AFM) modes supported by the MFLI lock-in amplifier. In combination with the MF-PID controllers, the MF-MD multi-demodulator option and the MF-MOD modulation option, the following AFM related functionality is supported:

  • 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 by enabling a feedback mechanism to quickly increase 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. 

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