RESISTANCE/RESISTIVITY PROBE
Contents
1. A description of the problem along with the contact name and telephone number must be included in formal paperwork and enclosed with the instrument Electro Tech Systems Inc will not assume responsibility for additional cost of repair due to damage incurred during shipment as a result of poor packaging 172. When establishing resistance resistivity requirements or when comparing resistance resistivity measurements the user must specify the test voltage Failure to do so could result in large measurement differences between different test set ups 3 3 2 3 Measurement Procedure The above information is provided to enable the user to make meaningful and accurate surface resistance resistivity measurements with the Model 803B Probe The following is a recommended procedure to be followed when measuring surface resistance resistivity 12 1 Determine the type of material being measured Use the precautions described in the previous sections 2 Make certain the contact electrodes are clean The electrodes may be cleaned with Isopropyl alcohol Allow electrodes to dry before using 3 Place the Probe firmly on the surface to be measured If the material to be tested is a film or foam additional pressure should not be required 4 Select the appropriate test voltage and resistance range 5 Observe the meter reading If it is unstable or the test material is rigid apply pressure to the Probe If the meter reading decreases continue to apply additional pressure until the reading stabilizes 6 If the meter reading remains stabilized for several seconds record the reading 7 If the meter reading continues to slowly increase wait until it stabilizes or for one minute before taking a reading 8 Repeat the above measurement proced
3. resistance may actually be very high but the measured resistance will be that of the surface resistance path between the two electrodes in parallel with the series combination of the two volume conductive paths and the conductive layer as shown in Figure 3 5 R Desired Surface R Volume Resistance CONDUCTIVE LAYER Figure 3 5 Resistance Path of Laminated Materials 3 3 2 For these materials only the net resistance is measured as defined in ESD 11 11 The actual surface resistivity cannot be accurately determined Another material type is the composite These materials generally consist of a high resistance resin loaded with conductive fibers or powders The surface resistivity of these materials is essentially not measurable What is actually being measured is the net resistance of the series parallel combination of the conductive component connecting the Inner and Outer electrodes A common problem that exists with this material is when the conductive component is buried just below the surface the top surface appears as a high resistance When the test voltage is increased to measure this high resistance the dielectric of the top surface breaks down and the meter then reads overscale The above precautions are presented to make the user aware of the complexity in making a surface resistance resistivity measurement It is not simply placing a probe onto a surface and reading a meter With care ma
4. Fixtures Models 809 809B and 819 These optional Fixtures are used to check the calibration of the Model 803B Probe Refer to Models 809 amp 819 Manual Figure 3 3 Optional Calibration Check Fixtures 3 3 Measurement of Surface Resistivity ps 3 3 1 Material Considerations The Model 803B Probe will accurately measure the surface resistance resistivity of virtually any smooth surface that is greater than 2 5 in diameter For most film and foam materials the standard 5 pound 2 2kg Probe weight is sufficient for the electrodes to make total contact with the material surface For rigid materials such as table tops plastics cardboard etc additional force may have to be applied to the Probe to ensure total contact Microscopically these surfaces are generally not smooth and are uneven as illustrated in Figure 3 3 UNEVEN SURFACE ROUGH SURFACE Figure 3 3 Microscopic Electrode Rigid Surface Contact In most cases the application of additional pressure will cause the measured resistance reading to decrease This is a result of both lower contact resistance and the total electrode surface contact area greater number of parallel resistance paths The ETS Model 847 Press shown in Figure 3 4 enables the user to apply controlled pressure to the Model 803 Probe Figure 3 4 Optional Model 847 Press Another area that must be considered when attempting to make a surface resistance measurement is th
5. RESISTANCE RESISTIVITY PROBE Model 803B ey S rf StaNCE RESIS PROBE MODEL 8038 5 a a Operating Instructions electro tech systems inc www electrotechsystems com 3101 Mt Carmel Avenue Glenside PA 19038 Tel 215 887 2196 Fax 215 887 0131 6 08 1 0 INTRODUCTION There exist many applications where the resistance or resistivity properties of static dissipative and insulating type materials are required ANSI ASTM D 257 is a standard test method for measuring the D C RESISTANCE OR CONDUCTANCE OF INSULATING MATERIALS This test method covers direct current procedures for determining the DC insulation resistance volume resistance volume resistivity surface resistance and surface resistivity of electrical insulating materials ANSI ESDA STM11 11 and STM11 12 are the latest standards for determining the surface and volume resistance characterization of planer static dissipative material respectively Variations of these test methods can be used to measure the resistance of conductive materials The resistance resistivity measurements are used for predicting the ability of insulating type materials to dissipate a buildup of electrostatic charge Materials that are coated chemically treated or contain an internal antistatic agent have static dissipative characteristics that are a function of the surface resistance resistivity On the other hand materials that are loaded with a conductive material suc
6. as t RC For total charging five times constants 5t is the accepted norm Therefore if a measurement system material has a total capacitance of 1 picofarad and a total resistance of 1 x 10 Ohms t RC 1 x 10 1 x 107 1 second The total charging time t 5 seconds This is the time of electrification It is seen that if the capacitance is only a few picofarads the time of electrification can stretch out to many seconds Figure 3 6 illustrates the time of electrification of an insulating type material Figure 3 6 Time of Electrification Resistance that is measured before the full time of electrification has occurred will be less than the actual resistance of the surface This difference can be several orders of magnitude ASTM D 257 recommends a time of electrification of 60 seconds but in many measurements a shorter time may be used or a longer time may be required Usually for small sample specimens with resistances less than 10 ohms an electrification time of 10 to 15 seconds is sufficient or the point at which the resistance measurement stabilizes On the other hand with large surfaces such as table tops the capacitance is relatively large and 60 seconds may not be long enough Here the user can either wait for complete electrification and obtain a true resistance measurement or specify the measurement at the 60 second electrification time point for a relative resistance measurement 11 In any case the t
7. e composition of the material being evaluated The materials defined in ANSI ASTM D 257 are homogeneous insulating types However in many specifications the materials are nonhomogeneous and relatively conductive If the material is static dissipative Rm lt 1x10 Ohms the measurement procedure defined in ESDA STM11 11 should be followed When measuring the surface resistivity of insulating homogeneous type materials the ground plane is used to guard against stray current paths that may cause measurement errors Materials that also have relatively low volume resistances cannot be measured using the procedure defined in ASTM D 257 Here instead of the current path between the two electrodes being only across the top surface it is also through the material to ground This creates a voltage divider network which results in a surface resistance measurement that will be higher than that obtained without the ground plane Therefore the surface resistivity of volume conductive materials cannot be made The test specimen must be measured on an insulated surface to obtain an accurate indication of its resistance characteristics as specified in ESDA STM11 11 A similar problem exists with materials that are coated with or laminated to a conductive surface In this case the test voltage is not divided down because the conductive layer is floating but the conductive layer now becomes a parallel resistance path to the surface being measured The surface
8. el 880 Resistance Indicator Features O Autoranging lt 10 to gt 10 O Autoselect test voltages 10 amp 100V O Built in parallel bar electrodes O Auxiliary probe input jacks O 10 measurement accuracy O Resistance to Ground Cable O Carrying case and Resistance to Ground O CE compliant Model 863 6487 Wide Range Resistance Meter Features O Range 509 to gt 10 Q O Adjustable Ve 0 2mV 505V O Alternating Ve polarity capability O 5 digit display O Up to 1000 readings second O Excel add in utility O EEE 488 amp RS 232 interfaces O Optional applications driver ICC nn a 6 08 16 6 0 WARRANTY Electro Tech Systems Inc warrants its equipment its accessories and parts of its manufacture to be and remain free from defects in material and workmanship for a period of one 1 year from the date of invoice and will at the discretion of Seller either replace or repair without charge F O B Glenside similar equipment or a similar part to replace any equipment or part of its manufacture which within the above stated time is proved to have been defective at the time it was sold All equipment claimed defective must be returned properly identified to the Seller or presented to one of its agents for inspection This warranty only applies to equipment operated in accordance with Seller s operating instructions Seller s warranty with respect to those parts of the equipment which are purchased from othe
9. h as carbon are volume conductive In most cases a material that is volume conductive is also surface conductive but there are certain composites or laminates where this rule does not hold true During the development of new static dissipating materials or coatings it is necessary to know the material resistance resistivity in order to predict the static dissipative characteristics Likewise it is also necessary to measure this parameter during the evaluation and qualification of existing materials where the expected resistance resistivity values are known In the static control applications a number of military industry and individual company standards exist that specify the surface and or volume resistivity as a material specification requirement Among these additional standards are ESDA standards requiring the measurement of surface and or volume resistance Mil Std 883 EIA 541 MIL PRF 81705D plus numerous company specifications such as those issued by Bellcore Hewlett Packard IBM Seagate etc ANSI ASTM D 257 describes several measurement techniques and measuring electrode types for determining resistivity The ETS Model 803B Resistance Resistivity Probe is a circular measuring electrode that is based around the concentric ring electrode design specified in the standard This electrode configuration shown in Figure 1 1 restricts the measurement path surface resistivity to just the area between the two concentric ring electrodes thu
10. ign of the Model 803B Probe electrode configuration is derived from the applicable formulas set forth in ANSI ASTM D 257 For the concentric ring design the surface resistivity Ps is a function of the ratio between the inner and outer ring diameters as shown in the following formula ps D D gt MRm Ohms sq D2 D1 D Outside Diameter of inner ring D2 Inner Diameter of outer ring Rm Measured resistance in ohms By properly choosing D and Do the factor D D2 D gt D1 can be made to equal any reasonable number In the case of the Model 803B 7 D D2 D2 D equals 10 resulting in a surface resistivity of Ps 10 Rm Ohms square The numeric value of ps is actually in Ohms The designation Ohms square clarifies the number as a surface resistivity measurement ESDA STM11 11 specifies a probe having the Model 803B design specifications Measurements however are made with the test specimen placed on an insulated surface instead of on a ground plane While surface resistivity is basically a function of the ratio between the inner diameter of the outer electrode and the outer diameter of the inner electrode the volume resistivity is basically a function of the area of the inner electrode and the thickness of the test specimen When measuring surface resistivity the test specimen is usually placed on a conductive plane and the resistance between the two electrodes measured On the other hand when measuring volu
11. ime of electrification is a critical parameter in the measurement of resistance resistivity and must be taken into account if meaningful results are to be obtained ESDA STM11 11 requires the determination of the actual electrification time as part of the measurement procedure 3 3 2 2 Test Voltage Certain materials are voltage dependent that is the resistance measured at one test voltage will not be the same as that measured with a different voltage Generally test voltages of 100 500 and 1000 Volts are used for very high resistances 10 Ohms and above while test voltages of 10 20 50 and 100 Volts are used for lower resistances in the range of 10 to 10 Ohms Some instruments use a single voltage to A STM11 11 specifies a test voltage of 100 Volts for material having surface resistances between 1x10 and 1x10 Ohms and 10 Volts for resistances between 1x10 and 1x10 Ohms Lower voltages or a current source may be used for resistances below 1x10 Ohms Another consideration is the contact resistance between the Probe electrodes and the material surface For certain materials especially those in the lower resistance range lt 10 ohms the contact resistance can be a factor At low ranges a test voltage of 1 5 Volts may used This low voltage may not be sufficient to breakdown the contact resistance Hence a significant difference in measured resistance may be obtained using 1 5 and 10 Volts and even 10 and 100 Volts
12. low 10 Ohms The same measurement procedures and precautions as mentioned above should be observed The Model 803B Probe can also be used in other applications such as obtaining an indication of the surface resistance to ground True surface to ground measurements can only be made using a 2 5 64mm diameter 5 Ib 2 2kg probe such as the ETS Model 850 Surface Resistance Probe In this application one side of the ohmmeter is connected to the Inner electrode Black banana jack and the other side to ground 4 0 MAINTENANCE The Model 803B Resistance Resistivity Probe is a precision instrument and should be handled as such The alignment of the Inner and Outer electrodes is critical to ensure total surface contact The silicon rubber contact material is impregnated with carbon nickel to obtain low contact resistance The user must ensure that the contact area is clean and free of contaminants prior to making a measurement Also the Probe should not be exposed to atmospheres or surfaces that may corrode the carbon nickel particles If exposure is necessary the contacts should be cleaned with Isopropyl alcohol immediately after use 14 5 0 When not in use the Probe should be kept on a flat smooth surface such as the test bed The Probe should never be kept on a sharp or protruding object since this may damage or put a set in the silicon rubber electrodes If the contact electrodes are damaged or the Probe knocked out of alignment the
13. me resistivity the resistance between the inner electrode and the conductive plane which is no longer grounded but is now the voltage electrode is measured The outer electrode then becomes the guard electrode when connected to ground per ASTM D 257 ESDA STM11 12 defines the test method for measuring volume resistance of material using a probe with the same design specifications as the Model 803B Measurements however are made with the outer electrode not connected The volume resistivity py must always be calculated because the thickness of the test specimen is one of the measurement variables The ANSI ASTM D 257 formula for py is Pv A Rm Ohms cm t A Area of measuring electrode in cm t Thickness of test specimen in cm Rm Measured resistance in Ohms For the Model 803B Probe the area of the measuring electrode is 7 1 cm thus py 7 1 Rm Ohms cm t The Model 803B Probe is fabricated from solid brass that provides weight and also helps provide shielding when making high resistance measurements The electrodes are mounted on Teflon insulators to provide high insulation resistance between the electrodes under relatively high humidity conditions This construction results in a 5 lb probe measuring 3 25 in diameter by 4 high 3 0 The compliant electrode contact material is carbon nickel impregnated silicon rubber with a hardness of 55 10 Durometer resulting in good probe surface contact For most materials the
14. need to apply additional pressure is eliminated The resistance of the electrode contact material is less than 1 Ohm The Probe is capable of measuring resistance from lt 10 to gt 10 Ohms The Model 803B Resistance Resistivity Probe comes complete with a 4 square aluminum plane with insulated feet an acrylic plane plus the necessary cables for connecting the Probe to any resistance meter with standard 0 162 4mm banana jack inputs OPERATION 3 1 3 2 Instrumentation The Model 803B Resistance Resistivity Probe can be used with any ohmmeter or resistance measuring apparatus that is capable of measuring within the desired resistance range The Probe has three standard banana jacks for connection to the measuring instrument The inner and outer electrodes are connected via standard black and red banana plugs respectively A third Ground jack is installed on the outer shell of the Probe Appendix A describes several resistance measuring instruments offered by ETS Equipment Setup 3 2 1 Surface Resistance and Surface Resistivity Figure 3 1 shows a typical Model 803B Probe hookup to a resistance meter for measuring surface resistance resistivity The Teflon sense cable is connected to the Inner electrode Black Jack and the voltage cable is connected to the Outer Electrode Red Jack The ground plane is connected to the ground on the meter Also the outer shell of the Model 803B Probe is connected to ground This ground connec
15. ny different types of materials can be evaluated but again the user is cautioned that the reading obtained may not be the true surface resistivity defined in ANSI ASTM D 257 ESDA STM11 11 circumvents this problem by defining only the net resistance of the material being measured Only if the material is truly surface conductive can this resistance measurement be converted to surface resistivity by multiplying the measurement by a factor of 10 Measuring Considerations 3 3 2 1 Time of Electrification In the previous section the effect of contact pressure which actually changes the contact area on the measurement accuracy was discussed Another very important consideration that many times is ignored is what is referred to as the time of electrification In simple terms the time of electrification is the time for current to flow between the measuring electrodes All materials have in basic terms some capacitance When measuring low resistances this capacitance is negligible in relation to the resistance of the material Therefore the current flow becomes restricted by the resistance of the material only On the other hand for high resistance measurements current flow is controlled by both the resistance and capacitance of the material The resistance does not begin to dominate the measurement until the exponential charging of the measurement system and material capacitance has been completed 10 The time constant t is expressed
16. r manufacturers shall be subject only to the manufacturer s warranty The Seller s liability hereunder is expressly limited to repairing or replacing any parts of the equipment manufactured by the manufacturer and found to have been defective The Seller shall not be liable for damage resulting or claimed to result from any cause whatsoever This warranty becomes null and void should the Model 803B Resistance Resistivity Probe or any part thereof be abused or modified by the customer of if used in any application other than that for which it was intended This warranty to replace or repair is the only warranty either expressed of implied or provided by law and is in lieu of all other warranties and the Seller denies any other promise guarantee or warranty with respect to the equipment or accessories and in particular as to its or their suitability for the purposes of the buyer or its or their performance either quantitatively or qualitatively or as to the products which it may produce and the buyer is expected to expressly waive rights to any warranty other than that stated herein ETS must be notified before any equipment is returned for repair ETS will issue an RMA Return Material Authorization number for return of said equipment Equipment should be shipped in the original packaging If this is not possible the equipment should be packed in a sufficiently large box of double wall construction with substantial packing around all sides
17. s eliminating measurement errors attributed to stray current paths such as those experienced with parallel bar electrodes The Model 803B is designed such that the measured surface resistance is converted to surface resistivity by multiplying the resistance measurement by a factor of 10 ESDA STM11 11 defines a specific ASTM D 257 type concentric ring probe for use in measuring the surface resistance of static dissipative material in the range of gt 1x 10 to lt 1 x 10 Ohms 2 0 ESD DS11 12 utilizes the inner electrode of the 11 11 Probe in conjunction with a flat metal plate electrode to measure volume resistance Variations of this procedure enable resistance in the conductive range to also be measured Figure 1 1 Model 803B Resistance Resistivity Probe EQUIPMENT DESCRIPTION The Model 803B Resistance Resistivity Probe design has been adapted as the industry standard for measuring the resistance characteristics or planar material This concentric ring probe incorporates a geometrical configuration that provides a x10 multiplication factor to convert the surface resistance measurement to surface resistivity The Probe is also capable of measuring volume resistance and volume resistivity of material having smooth flat surfaces of at least 2 5 diameter The ability of the Model 803B Probe to measure materials of this size makes it compatible with the standard specimen size used in most electrostatic parameter testing The des
18. tion is not necessary for resistances less than 10 ohms If a meter with only two output connections is used connect the HI side usually red to the Outer electrode and the LO side usually black to the Inner electrode Resistance Meter GND OHMS 4 SYS GND N Test Sample ne ee ae eee Gnd Plane Figure 3 1a 803B Probe Resistance Meter Hookup for Surface Resistivity Measurement D257 Resistance Meter GND OHMS 14 YS GND SYS Gi e Test Sample Insulated Acrylic Plane Figure 3 1b 803B Probe Resistance Meter hookup for Surface Resistance Measurement ESDA STM11 11 3 2 2 Volume Resistivity Figure 3 2 shows typical Model 803B Probe hookup to a resistance meter for measuring volume resistance resistivity The Teflon sense cable is connected to the Inner electrode Black Jack and the voltage cable is connected to the plate The same plate as is used for the Ground plane for surface resistivity The Outer electrode Black Jack is connected to ground D257 along with the outer shell of the Probe for measuring the volume resistivity of insulating material For static dissipative material per ESD DS11 12 the Outer electrode is_not connected Resistance Meter OHMS 1 Y ND SYS G T Test Sample Gnd Plane Figure 3 2 803B Probe Resistance Meter Hookup for Volume Resistance Resistivity Measurement STM11 12 3 2 3 Surface and Volume Resistance Calibration Check
19. unit must be returned to ETS for repair The Probe does not contain any user replaceable parts The optional ETS Models 809 and 819 Calibration Check Fixtures enable the user to verify the integrity and correct alignment of the electrodes prior to use For measurements below 10 Ohms standard banana plug to banana plug cables may be used However for measurements above 10 Ohms a high resistance such as Teflon cable must be used for the sense lead Replacement cables are available from ETS Wide Range Resistance Meters ETS offers the following wide range resistance meters that conform to specifications referencing the concentric ring probe Model 871 Wide Range Resistance Meter Features O Measurement range 1x10 5x10 Q 10V 1x10 5x10 Q E 100V O Autoranging O Accuracy better than 2 O Large 2 line alphanumeric display O Remote measurement activation O Compatible with most resistance probes O PC compatible COMM port O Battery or AC powered 15 Model 873 Wide Range Resistance Meter Features O Measurement range 10 to 10 Q 10V 10 to 10 Q E100V O Autoranging microcomputer based O User selectable regulated test voltages O 2 line alphanumeric LCD display O Configurations available Meter only With plug in surface volume electrode assembly Kit with required accessories O Battery and optional AC power O Meets ESDA ASTM SAE J1645 DOD plus International requirements Mod
20. ure at different locations across the material surface 9 The surface resistivity is 10 times the measured resistance ps 10Rm Follow the procedure described in ESDA S11 11 for measuring the surface resistance of static dissipative planer material 13 3 4 Measurement of Volume Resistivity py The same parameters electrode contact pressure time of electrification excitation voltage and material composition must also be taken into consideration when measuring the volume resistivity py of materials The volume resistivity of a material is defined as the resistance through a one cubic centimeter of material The user is cautioned that a relatively low resistance measured through a very thin film may actually describe a material with a very high volume resistivity To measure the volume resistance resistivity of a material the same testing procedure described in Section 3 3 2 3 should be followed To obtain the volume resistivity the thickness of the test material must be measured using a metric micrometer or converting the English measurement to metric 1 mil 2 54 x 10 cm The volume resistivity using the Model 803B Probe is then Pv 7 1 Rm Ohms cm t Follow the procedure described in ESDA STM11 12 for measuring the volume resistance of static dissipative material 3 5 Other Applications The Model 803B carbon nickel impregnated electrodes have a very low contact resistance It is capable of measuring resistances be
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