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What is the field uniformity across the sample stage in the vertical probe stations?
Field uniformity (or homogeneity) for the CPX-VF and CRX-VF stations is 0.5% over a 10 mm diameter and 1% over 25 mm diameter. For those interested in seeing field uniformity plots, Lake Shore can provide BZ contour plots of percent deviation of the field on or 1 mm above the grounded sample holder in a CPX-VF or CRX-VF station. To obtain these plots, contact Sales at email@example.com.SlideUp
In a CPX or CRX probe station, do you have any guidance on how to avoid contamination of a delicate sample during cool down to helium temperatures?
For helium temperature operation, residual gases in the probe station chamber will condense and freeze on the coldest surfaces, and, under normal operating conditions, the sample stage is often the fastest cooling stage of a cryogenic probe station. You can avoid contamination on your sample by maintaining the sample stage at room temperature during station cool down. An effective way to minimize the condensation on the sample, this procedure is often required when measuring a surface-sensitive sample, as well as any device where maintaining low contact resistance is critical. This is accomplished by allowing the radiation shield stage to cool first so that the majority of residual gas is attracted to it and not the sample mounted on the sample stage. Specifically, the temperature controller, which is used to precisely regulate sample stage and radiation shield temperatures, will keep the sample stage warm while the remainder of the refrigerator cools to base temperature, at which point, any residual gas in the chamber will condense on the 4 K shield stage. The step-by-step procedure for doing this can be found in Chapter 5 of the probe station manual. This feature is only available on CPX and CRX probe station models.SlideUp
When characterizing a sample with delicate contact electrodes in a probe station, which type of probe tip material is best to use and ensure the best electrical contact performance?
Lake Shore offers three different types of probes distinguishable by their probe tip material. For delicate or softer contact materials (such as gold), beryllium copper (BeCu) probes are recommended. These are the softest probe tips offered, providing conventionally the lowest contact resistance and the smallest amount of deformation to the contact metallization. Over time, the BeCu material is known to form a semi-insulating layer which can diminish contact performance; see Section 6.2.7 of your probe station manual for maintenance protocols for this probe material. This probe material is available on both standard DC/RF and continuously variable temperature (CVT) probes. At the other extreme, for aluminum, refractory metals, and other material contacts that develop oxides, a standard ZN50 tungsten probe will best puncture hard oxide material layers to make electrical contact with underlying layers and will not dull as quickly as softer probe materials. Because the spring member on the CVT probe reduces the pressure at the tip apex, tungsten CVT probes may have difficulty punching through hard insulating layers and are not recommended for oxidized contacts (such as aluminum). A good intermediate solution between beryllium copper and tungsten is a paliney probe tip material offered on Lake Shore’s standard DC/RF probes. A paliney probe offers low contact resistance but a little bit stronger of a probe tip material (while also being the least reactive material and are least likely to form resistive oxides, especially at high temperatures).SlideUp
I am looking for information about calibrating my VNA for microwave measurements in a Lake Shore probe station. Are there any general recommendations on calibration methods?
To calibrate out the dispersion and losses of the probes as well as probe station and network analyzer cabling, most network analyzers support a SOLT (short-open-load-through) calibration. For probing measurements, a CS-5 on-wafer calibration substrate (available from Lake Shore) is used as the reference standard for the calibration. Before performing the calibration at a given sample stage temperature, GSG probes should be planarized to the calibration substrate. Once the prober has been calibrated, the frequency-dependent S-parameters of your wafer-level DUT can be determined. The SOLT calibration method is sufficient for most conventional microwave on-wafer probing applications below 20 GHz. For higher-frequency measurements, however, other calibration methods may be necessary. Above 20 GHz, the SOLT method is extremely sensitive to consistent probe placement and contact pressure in order to achieve an accurate calibration. For better S-parameter accuracy at higher frequencies, Lake Shore recommends TLR (thru-reflect-line) or LRRM (line-reflect-reflect-match) on-wafer calibration techniques to reduce the impact of probe placement errors. These calibrations can be carried out using the WinCal software package in conjunction with calibration substrates from Cascade Microtech. However, the LRRM calibration method is more sensitive to the variation in load standard; for cryogenic measurements, the temperature-dependent load resistance should be measured and compensated in the calibration calculation.SlideUp
When setting excitation current in my Hall system, I want the current high enough that the desired voltage is large compared to the unwanted signals but not so high that it adversely affects my measurement and damages my sample. How can this be done?
This is a multi-step process. First, use the toolbox resistance measurement to find a current the produces a voltage across the contact between 0.1 volt and 0.01 volt. This is a range that we find useful, but you may have to move out of this range depending on the material and the contacts. We typically start at a milliamp of current and move up or down from there to find a starting voltage. For the sake of discussion, assume the current is 10 microamps. Then go to measurement section and select only ohmic check. Set the max. current to value selected in the toolbox (10 microamp in this case) and the min. current to 1/10th of the max. current (1 microamp in this case). Set the number of points 5 and run the ohmic check. If the correlation is 0.9999 or higher, you are good to go. If the correlation coefficient is less than 0.9999, try decreasing the max. current and min. current by a factor of 3 and repeat the ohmic check. The purpose of this is to eliminate self-heating, which will distort the linear ohmic check. This is particularly important if the AC field option is used. Self-heating during an AC field measurement can inject noise into the measurement. Sometimes, decreasing the current used in the AC field measurement can increase the signal to noise ratio of the measurement.SlideUp
Where exactly is the active area on a Hall probe?
The active area is the effective area over which the Hall sensor averages the magnetic field. Knowing where it is can be a concern for users who are trying to measure magnetic fields exhibiting large field gradients. It’s also important to know when performing magnet pole surface testing, where there can be a dramatic falloff of field strength near the surface. In this case, only a few thousandths of an inch difference in distance between the sensor active area and the magnet surface may change the gaussmeter reading by more than the tolerance allowed. The active area is also something to keep in mind when ordering probe, too. Because Hall probes measure an average magnitude over their active area, it’s important to understand the relationship between active area and field gradients.SlideUp
Model 425 Gaussmeter monitor output
There may be a slight, very minimal delay, but we have not measured and specified it nor do we understand if the delay remains the same throughout the various measurements (AC or DC). If you're observing a delay in measurement, it could also be due to the settling time of the measurement signal. The entire measurement stage is AC-coupled to get rid of DC offsets.SlideUp
unable to update settings after firmware update
We've seen similar before and a reset to factory defaults should fix the issue. To reset the instrument to the factory defaults: 1. Tap the Settings menu (top left corner of the screen). 2. Tap System settings. 3. Tap Reset, then tap Reset instrumentation settings. 4. A confirmation message will appear. Tap Reset to confirm the action. If you continue having issues, please contact us at firstname.lastname@example.org for further troubleshooting.SlideUp
Can you first confirm that you're using a pulse-discharge magnetizer for this operation? It should be possible to do what you are asking about and the first thing to do is to make a custom coil such that it is sensitive enough to produce a measurement but at the same time doesn't overload the instrument's input (pulse X # of turns) upon discharge. Are you able to wind your own coil? The Model 480 has an absolute limit of 100V to the input but we recommend staying at or below 60V. Once you have a coil that works properly to measure the pulse, automation via custom software can be achieved. You would need to write your own software that can communicate over GPIB. Besides using standard and common programming languages, LabVIEW would also be one of your options.SlideUp
425 Gaussmeter Measurement
Please tell me if the measurement was ever correct. Also, do you have a different probe or gaussmeter that you can compare the measurements with? If anything is wrong, it most likely is the probe. The Hall sensor is in the tip and it is VERY sensitive. Abrasion, shock, etc., will damage the sensor easily which would cause such unexpected measurements. What happens when you zero the probe? Do you get a "larger offset than expected" error message at the end of the zeroing process?SlideUp
Adding a sensor curve without a serial number isn’t working properly when using the CRVHDR command. Why is this?
The instrument ignores spaces and commas when parsing the CRVHDR command. Therefore, you need to enter a term in the serial number field even if the sensor doesn’t have a serial number. An example command that will work reliably for a sensor without a serial number would be CRVHDR 21,SENSOR21,NONE,4,325,1 where NONE is used as the serial number.SlideUp
How often should cryogenic temperature sensors be recalibrated?
There are no specific published regulations or guidelines that establish requirements for the frequency of recalibration of cryogenic sensors. There are certainly military standards for the recalibration of measuring devices. However, these standards only require that a recalibration program be established and then adhered to in order to fulfill the requirements. Many highly regarded manufacturers of more complex measuring devices, such as voltmeters, recommend that such instruments be recalibrated every six months. Temperature sensors are complex assemblies of wires, welds, electrical connections, dissimilar metallurgies, electronic packages, seals, etc., and hence, have the potential for drift in calibration. Like a voltmeter, where components degrade or vary with time and use, all of the “components” of a temperature sensor may also vary, especially where they are joined together at material interfaces. Degradation in a sensor materials system is less apparent than deterioration in performance of a voltmeter.SlideUp
With negative temperature coefficient (NTC) temperature sensors, is higher resistance better?
For both germanium and Cernox RTDs, there is a common misconception that a higher resistance equates to a “better sensor,” if that is interpreted to mean a sensor that has better resolution or better accuracy (i.e., lower uncertainty). It is important to understand that concepts of resolution and accuracy are largely meaningless if applied only to the temperature sensor. These concepts become meaningful only when discussed in the framework of the electronics used to measure their resistance. Many instrumentation subtleties affect low temperature thermometry measurements, including the excitation mode and how the instrument switches between resistance ranges. Ultimately, the excitation level and resistance range determine the electronic resolution and accuracy which, in turn, determine the temperature resolution and accuracy. Since for a given NTC thermometer type, higher resistance implies higher sensitivities, it would be expected that the higher resistance thermometers should yield better resolution and accuracy.SlideUp
What is the procedure for testing a diode sensor?
Ensure that your multimeter is rated to measure resistances up to 10 megohms, then follow this test procedure: 1. Verify diode (part 1) Place the positive (+) lead of your multimeter on I+ or V+ and the negative (-) lead on V- or I. You should measure approximately 5 megohms at room temperature. 2. Verify diode (part 2) Place the negative (-) lead of your multimeter on I+ or V+ and the positive (+) lead on V- or I. You should measure an “open” (infinite resistance). 3. Verify sensor leads: measuring between the I and V leads - Measure the resistance between the I+ and V+ leads. You should measure the total resistance of your wire. - Measure the resistance between the V- and I- leads. You should measure the total resistance of your wire. 4. Verify sensor leads: isolation - Place one lead of your multimeter on I+ or V+ and the other lead to your system ground. You should measure an “open” (infinite resistance). - Place one lead of your multimeter on I- or V- and the other lead to your system ground. You should measure an “open” (infinite resistance).SlideUp
Calibration Intervals for Silicon Diodes
The decision on whether to recalibrate your sensors depends on your internal processes and quality department requirements. As you state, the diode sensor is very stable over the long term, however, many customers that use our sensors to perform controlled measurements for their customers return them annually where other customers never have them recalibrated. Our temperature sensors come with a 3-year warranty, therefore, if something in the sensor construction or material fails causing the sensor to shift in calibration, it would be recalibrated or replaced under warranty.SlideUp
We were using the model SHI-4-2, and we noticed that the vibrations were conducted to the sample holder and the optical table. Is that the normal case which the pump of the system vibrates the table, or we probably missed something? Does anyone have the same issue?
Thank you for submitting your question, I apologize for the delayed reply. The model SHI-4-2 is not a vibration isolated cryostat and I would expect that the vibrations caused by the coldhead and coming from the compressor through the helium flexlines would cause serious issues. Is this something new? Has the cryostat been moved so that it is now on your optical bench? Also, having the serial number of your cryostat might help.SlideUp
cold head model M22 temperature sensor reparation
Is this a Janis Cryostat? If you contact us it is always nice to have the Janis serial number of your cryostat. Yes, the flexlines should be disconnected when everything is at room temperature. Note that the fittings used in these systems are Aeroquip fittings, these are zero-dead volume, self-sealing fittings. When these are properly made up or disconnected there should be no loss of helium.SlideUp
I am writing an application that controls a 155 I/V source via SCPI. After a while the display's auto-dimming kicks in and I can't figure out how to light up the display. I tried the SCPI commands to adjust the brightness and turn the display on and off without any luck. Is this feature available?
There is at the moment no way to turn this off but I've let our engineers know to consider this in a future firmware update. Currently, the timer is set to 30 minutes and the display needs to be touched to bring it to light back up.SlideUp
Is saddling (centering) the sample important for a magnetometer, especially with a VSM?
Yes, because the position of the sample will directly affect the detection efficiency and, in turn, the accuracy of the moment values. If you don’t saddle it by positioning the sample at the center of the detection, the moment value will be incorrect. Your measurement will be only qualitative not quantitative – that is, you see the shape, but you cannot rely on the numbers of the measurement. For more guidance on this, see Section 4.3.3. in the 7400-S Series VSM user manual, which shows moment vs. position on all three (X-Y-Z) axes. It explains how much moment is affected by a sample being off-center.SlideUp
Is cooling water always needed for VSM operation?
Yes, because both the electromagnet power supply and the electromagnet itself need cooling to dissipate the heat during operation. The water flow values are very important. You cannot do even a limited field range type of measurement without cooling.SlideUp