The Multi Height Probe combined with the HM21 Hand Held Meter is a great system for use in measuring a wide range of materials and sample sizes when the greater measurement range of the RM3000 Test Unit is not necessary.
The Multi Height Probe
The probe portion of the system, the Multi Height Probe, comprises a hard anodized aluminum base 25cm wide, 29cm deep and 0.8cm thick. A 19mm diameter stainless steel column 20cm high screwed to the base supports the probe head raising and lowering mechanism incorporating the vertical slide, operating lever shaft, and micro-switch.
The vertical slide carries the probe-head, secured by a clamp screw. The probe-head is positioned so that the micro-switch does not pass current until the probes have made contact, lost motion ensures that the current is switched off before the probes are raised. The probe arm can be easily positioned on the vertical shaft to various heights to allow probing onto either flat materials or large or thick materials. For example, a shallow dish containing LN2 could be placed on the base plate and the arm could be positioned to allow the probe to be lowered onto a sample submerged in liquid nitrogen.
Materials up to 10″ x 10″ can be positioned under the probe arm (or with a 12″ x 12″ working area for the same price), ingots, and materials that are up to 6″ tall. If necessary, a taller vertical post can be supplied for use in measuring taller items. The Cylindrical probe head, one of which is included with the Multi Height Probe, can withstand temperatures from 77K up to 120C in it’s standard configuration. A modification to the Cylindrical probe will allow it to withstand temperatures from 77K up to 200C in an oven, or up to 300C for short periods of time on a hot chuck. The Multi Height Probe is conservatively limited to 80C, however, temperatures up to 300C using a hot plate are okay if certain precautions are taken.
Optionally, at no additional charge, the Multi Height Probe can be supplied with four mounting holes so that it can easily be upgraded in the future to add either 1) the 25mm travel X-Y sample stage with 76mm (~3″) diameter vacuum hold-down sample chuck for use in positioning very small samples under the probe tips, or 2) the 6″ or 8″ wafer stages which can be seen on page 3 of the PDF file mhp+hm21.pdf. When a wafer stage is supplied with the Multi Height Probe, it can be removed for use in measuring other types of materials, however, it does not include the integral light shield which is provided with the Multiposition Wafer Probe systems.
The system incorporates the Jandel Cylindrical probe head which is built to high standards of quality and accuracy. A brochure regarding the Cylindrical probe can be found here: https://four-point-probes.com/jandelcylindrical.pdf
Information regarding the constructions and specifications of the Jandel Cylindrical probe can be seen here:
https://four-point-probes.com/cylindrical_app_notes.pdf
HM21 Hand Held Meter
The Jandel HM21 Hand Held Meter is a battery powered four point probe meter which includes a universal AC power adapter so that it does not have to run on batteries when portability is not important. The Jandel HM21 is a portable current source / meter specifically designed for the four point probe measurement technique. For successful measurements the HM21 supplies a constant current and displays either the resultant voltage or the sheet resistance in ohms/square depending which function has been chosen.
The sheet resistance measurement range is 1 ohm/square up to 10 Megohms/square (in practice you can measure down to around 0.01 ohms/square, but the accuracy may be compromised slightly). This equates to a bulk (or volume) resistivity range of approx. 0.01 ohm.cm to 100 Kohm.cm. The current is changeable in 6 steps – 100nA, 1uA, 10uA, 100uA, 1mA, 10mA. The compliance voltage is above 8.5V but slightly reduces to 7.5V at 10mA, however 10mA would usually only be used with more conductive samples where the compliance voltage is not so critical.
Overall accuracy is better than 0.5% where the DVM receives greater than 1mV. For the mid ranges the accuracy is better than 0.3% The DVM has two ranges – high sensitivity up to 150mV and low range up to 1.25V.
The unit is push button operated. The current is increased with the ‘INC’ button and decreased with the ‘DEC’ button. Forward and reverse current can be selected using the ‘FWD’ and ‘REV’ buttons, which is a common way to check the validity of a measurement by checking the forward and reverse voltage values for consistency. When the battery mode is used, the unit returns to standby automatically to save power and turns off altogether after some period of inactivity.
The automatic time to return to standby is 70 seconds with low current and with the 3 highest currents 40 seconds. This is because the lower current ranges are used with higher impedance which can take longer to settle, and the higher currents drain the power faster. The unit can be zeroed to remove any offset by pressing the Standby button when the unit is already in Standby.
The HM21 includes on-board non-volatile memory so that fifty measurements can be stored in the unit and then downloaded to a PC later. When connected to a PC using the included software, the HM21 can save the data, or bulk resistivity values (ohms-cm) can be calculated. If the HM21 is connected to a PC using the software, the unit can be operated via the user interface which is an illustration of the HM21 on the computer screen. Clicking the “save” button on the computer screen saves the data to the PC. Files are stored in the CSV format which opens automatically in Excel. The HM21 reads-out directly in sheet resistance (ohms-per-square) without using a PC or the software.
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We Recommend
The Multi Height Probe with the RM3000 Test Unit features high accuracy, an excellent range, and many features which simplify the four point probing measurement:
Multi Height Probe combined with the RM3000 Test Unit.
Four-Point-Probes is a division of Bridge Technology. To request further information please call Bridge Technology at (480) 219-9007 or send e-mail to Joshua Bridge at: sales@bridgetec.com
