Miller 400A User Manual
Contents
1. Conveniently for both M C Miller soil boxes the A L ratio is exactly Consequently when M C Miller soil boxes are used the resistance reading in ohms determined using the MILLER 400A becomes the resistivity value in ohm cm If the resistivity value is required to be expressed in ohm m rather than ohm cm the ohm cm value is divided by 100 For example a resistivity value of 2500 ohm cm would be equivalent to 25 ohm m 3 ELECTRODE APPLICATION The 3 Electrode Application can be used to measure the resistance to earth of a buried electrode such as a buried ground rod or a buried anode In this case two of the electrodes are pins driven into the earth and the third electrode is the test electrode itself for example a ground rod or an anode A resistance to earth measurement will actually comprise 3 components the resistance of the electrode itself the resistance of the ground rod or anode material for example including test leads the electrode earth contact resistance and the resistance of the surrounding earth Typically the resistance of the surrounding earth is the largest component of the resistance to earth measurement The three electrodes are positioned in a straight line ideally as indicated in Figure 3 below Page 10 of 14 3 ELECTRODE APPLICATION ELECTRODE GROUNDING ROD or ANODE RESISTANCE TO EARTH MEASUREMENT RESISTANCE Potential Current Electrode Electrode Anode or Grounding Rod2. Figure 3 As indicated in Figure 3 a jumper wire is connected between the C1 and P1 terminals on the MILLER 400A and test leads connect the Potential Electrode and the Current Electrode to terminals P2 and C2 respectively Finally a test lead connects the electrode under test a ground rod or an anode for example to the C1 terminal With this configuration the MILLER 400A passes a current between the test electrode and the Current Electrode and generates a resistance reading based on the voltage dropped between the electrode under test and the Potential Electrode The magnitude of the resistance reading will be a function of the separation distance between the electrode under test and the Potential Electrode with respect to a fixed position for the Current Electrode Page 11 of 14 A characteristic resistance versus distance plot is illustrated in Figure 4 below A characterisitic resistance versus distance plot assuming that the Current Electrode see Figure3 is far enough away from the electrode under test gt Aw 39 G lt ES ou cul s sz a Distance between the electrode under test and the Potential Electrode see Figure 3 feet Figure 4 This type of plot assumes that the Current Electrode see Figure 3 is positioned far enough away from the electrode under test so that a plateau region is obtained in the plot A 100 foot separati
3. 4 While holding the Null Sensitivity switch in the Low position step down through the resistance ranges 10K 1000 etc until the needle moves to the left of the null position left of the center position and then step back up one range 5 Adjust the position of the Balance Dial until the needle is positioned at the null center location on the meter 6 Multiply the Balance Dial setting by the range setting setting on the switch labeled Ohms Multiply By to obtain the resistance value For example for a Balance Dial setting of 4 5 and a range switch setting of 1000 the resistance value is 4500 7 Apply the resistance value to the calculation of resistivity using the appropriate formula for your application see the Applications section below Page 5 of 14 Note You can increase the sensitivity of the resistance reading by holding the Null Sensitivity switch in the High position and fine tuning the balance after finding the balance point in the Low sensitivity position APPLICATIONS 4 ELECTRODE APPLICATIONS 1 Earth Resistivity Measurement This application uses 4 electrodes pins The electrodes are driven down into the earth the same distance and are evenly spaced in a straight line A schematic of this arrangement is illustrated in Figure 1 below 4 ELECTRODE APPLICATION EARTH RESISTIVITY MEASUREMENT RESISTANCE Ohms Figure 1 Page 6 of 14 The MILLER 400A can b
4. In this case the two electrodes are the two buried components Figure 5 below illustrates the measurement configuration Page 13 of 14 2 ELECTRODE APPLICATION RESISTANCE MEASUREMENT BETWEEN TWO ELECTRODES GROUND RODS or ANODES RESISTANCE Ohms Anode or Anode or Grounding Rod Grounding Rod Figure 5 As indicated in Figure 5 in this configuration jumper wires are connected between terminals C1 and P1 and between terminals C2 and P2 In addition test leads connect one of the electrodes to terminal C1 and the other electrode to terminal C2 Another configuration option which is recommended for use when measuring small resistances is to connect the potential terminals P1 and P2 directly to the electrodes with separate test leads thus eliminating the jumper wires Such a configuration eliminates any voltage drop in the test leads due to current flow in the leads which would appear in series with the voltage drop occurring between the electrodes in the case of the configuration shown in Figure 5 The resistance reading determined by the MILLER 400A will be a direct measurement of resistance comprising 2 components the resistance to earth contribution of each electrode which itself comprises 3 components see the Page 14 of 14 3 Electrode Application section above and the earth s resistance between the two electrodes MAINTENANCE amp CALIBRATION Other than changing the batteries the MILLER 400A requires n
5. Page 1 of 14 MILLER 400A ANALOG RESISTANCE METER PART 44500 USER S MANUAL IMIG MILLER co M C Miller Co Inc 11640 U S Highway 1 Sebastian FL 32958 U S A Telephone 772 794 9448 Website www mcmiller com Page 2 of 14 Description CONTENTS Operating Instructions Applications Ene TOM RP T ER dI 4 Electrode Applications Earth Resistivity Measurement Electrolyte Soil Box Measurement 3 Electrode Application 2 Electrode Application Maintenance amp Calibration Page 3 of 14 DESCRIPTION When combined with appropriate electrodes pins and test leads the MILLER 400A can be used to measure earth resistance or the resistance to earth of a buried electrode such as a ground rod or an anode for example Depending on the application 4 Electrode 3 Electrode or 2 Electrode the MILLER 400A can be used to determine the following e The average earth resistivity to a specific depth with the application of an appropriate multiplier to convert resistance to resistivity based on the electrode separation distance 4 Electrode Application e The resistivity of a soil sample or of a liqu
6. e used in conjunction with M C Miller s 4 lead color coded test reel catalog 44700 and four heavy duty stainless steel electrodes soil pins catalog 44720 The test leads are connected to the MILLER 400A as shown in Figure 1 With this arrangement the MILLER 400A effectively measures the earth s average resistance to a depth equal to the electrode spacing S Dr Frank Wenner of the U S Bureau of Standards developed the theory behind this test in 1915 1 He showed that if the electrode pin depth d is kept small relative to the separation between the electrodes S the earth s average resistivity to a depth equal to the electrode spacing S can be obtained by applying the following formula p 2nxSR where R is the resistance value in ohms as determined using the MILLER 400A p is the resistivity in ohm cm is the constant 3 1416 and S is the electrode separation in cm Typically the electrode pin spacing is not measured in centimeters but rather in feet in the U S or in meters in most other countries U S Example electrode spacing measured in feet Since there are 30 38 centimeters in 1 foot the above formula can be written as p Q cm 2r x 30 38 x electrode spacing in feet x R ohms or p Q cm 191 5 x electrode spacing in feet x R ohms So for example if the MILLER 400A produces a resistance value of 15 ohms for an electrode pin spacing of 20 feet the earth s average resistiv
7. id via an electrolyte soil liquid box with the application of an appropriate multiplier to convert resistance to resistivity depending on the box geometry 4 Electrode Application e The resistance to earth of a buried electrode such as a ground rod or an anode for example 3 Electrode Application e The resistance between two buried electrodes such as two ground rods or two anodes 2 Electrode Application The current source in the MILLER 400A which supplies current between the and C2 terminals with a load applied is a 12V rms crystal controlled 97Hz square wave oscillator and the voltmeter inside the unit which senses the potential difference voltage drop appearing across the P1 and P2 terminals employs a very narrow band pass filter centered at 97Hz What this means is that resistance measurements taken by the MILLER 400A are unaffected by any stray interference signals having frequencies other than 97Hz that may be present in the earth during a measurement The MILLER 400A has a resistance measurement range from 0 01 Ohm 0 019 to 1 1 MOhm 1 1 that is achieved by means of a set of 8 range settings and a system of internal standard resistors External resistances resistance values under test are compared against the internal standards via a null balancing system resulting in a determination of the external resistance values The MILLER 400A runs on a set of replaceable C size alkaline batte
8. ity value to a depth of 20 feet would be p 191 5 x 20 x 15 57 450 ohm cm If the resistivity value is required to be expressed in ohm m rather than ohm cm the ohm cm value is divided by 100 In the above example the resistivity would be 574 5 ohm m Page 7 of 14 Metric Example electrode spacing measured in meters Since there are 100 centimeters in 1 meter the above formula can be written as p 2n x 100 x electrode spacing in meters x R ohms or p 628 32 x electrode spacing in meters x R ohms So for example if the MILLER 400A produces a resistance value of 15 ohms for an electrode pin spacing of 7 meters the earth s average resistivity value to a depth of 7 meters would be 628 32 x 7 x 15 65 973 6 ohm cm If the resistivity value is required to be expressed in ohm m rather than ohm cm the ohm cm value is divided by 100 In the above example the resistivity would be 659 73 ohm m Note The above formula is accurate only if the electrode depth d is small relative to the electrode spacing S An S value equal to or greater than 20 times the d value is recommended This means that if d 15 1 foot for example then S has to be at least 20 feet or if d is 0 3 meter then S has to be at least 6 meters The Wenner Method 15 the basis of an ASTM Standard Test Method ASTM G57 78 2 Soil Sample Liquid Resistivity Measurement This application also uses 4 e
9. lectrodes however in this case the electrodes are an integral part of an electrolyte box which is more commonly referred to as a soil box For this application the MILLER 400A can be used in conjunction with one of M C Miller s soil boxes catalog 37008 or catalog 37006 and 4 test leads catalog 37009 A schematic of the test arrangement is illustrated in Figure 2 below Page 8 of 14 4 ELECTRODE APPLICATION SOIL or LIQUID RESISTIVITY MEASUREMENT VIA AN ELECTROLYTE BOX RESISTANCE Ohms ELECTROLYTE SOIL or LIQUID BOX Figure 2 For this application the test leads are connected to the MILLER 400A as shown in Figure 2 With this arrangement the MILLER 400A determines the resistance of the soil sample or of the liquid that fills the electrolyte box In general for a particular volume of soil sample or liquid as defined by the geometric constraints of the electrolyte box the sample s resistivity can be calculated from the resistance value determined using the MILLER 400A by applying the following formula p where p is the resistivity in ohm cm R is the resistance in ohms A is the cross sectional area of the current electrodes in cm squared and L is the separation between the potential electrodes in cm Page 9 of 14 Consequently the ratio A L represents a multiplication factor that needs to be applied to the resistance reading in order to obtain the sample s resistivity value
10. o maintenance When the Low Battery indicator lights up and remains ON during a balancing procedure the batteries should be replaced The procedure to change the 8 C size alkaline batteries in the unit is as follows 1 Remove the 4 screws on the front panel and lift the panel out of the plastic case 2 Turn the panel upside down and place on a clean and dry surface 3 Undo the four retaining clips and remove the two sets of 4 old batteries from their holder tubes 4 Insert 4 new C size alkaline batteries into each holder tube and reinstall the tubes making sure that the battery polarity 1s correct as labeled in each case 5 Re install the retaining clips 6 Re install the panel into its plastic case and re install the 4 screws on the front side of the panel With respect to calibration it is recommended that the MILLER 400A be returned to M C Miller for re calibration on an annual basis Reference 1 Wenner A Method of Measuring Earth Resistivity Bulletin of Bureau of Standards Report 258 Vol 12 No 3 Oct 11 1915 February 18 2011
11. on is typically recommended However it is suggested that a resistance versus distance curve be generated for any given situation in order to verify the existence of a plateau type region which will allow an accurate determination of the electrode to earth resistance Assuming that a plateau type region is obtained the resistance to earth value for the electrode under test will be the resistance value on the plot corresponding to the plateau region as illustrated in Figure 4 A general rule of thumb which assumes that the Current Electrode 15 positioned sufficiently far away from the electrode under test is that if the Page 12 of 14 Potential Electrode is positioned at a distance from the test electrode of 0 62 x D where D 15 the distance between the electrode under test and the Current Electrode the resistance reading observed will correspond to the resistance to earth value for the electrode under test This particular configuration is illustrated in Figure 3 For example if the distance between the electrode under test and the Current Electrode 15 100 feet the Potential Electrode should be positioned 62 feet from the electrode under test However again it is suggested that resistance versus distance plots be generated in each instance 2 ELECTRODE APPLICATION The 2 Hlectrode Application can be used to measure the resistance between two buried electrodes such as two ground rods or two anodes for example
12. ries so there is no requirement to periodically re charge the unit or to plug the unit Page 4 of 14 into a power source Please see the Maintenance section for information on how to replace the batteries OPERATING INSTRUCTIONS The test lead connections that are made to the Current terminals and C2 and the Potential terminals P1 and P2 depend on the particular application of the MILLER 400A The various connection requirements as well as the various accessories required in each application are detailed in the Applications section Regarding the applications that involve inserting electrodes pins into the earth it is recommended that the electrodes pins be firmly driven into the earth pins cannot be loose Also in dry soils it is recommended that the soil around the pins be moistened in order that reliable low resistance contact is made to the surrounding soil How to take a resistance reading 1 Connect the test leads and set up the electrodes pins as outlined in the Applications section for your particular application 2 When the approximate resistance say of the local soil is not known move the range selector switch labeled Ohms Multiply By to the 100K setting and position the Balance Dial knob at 10 3 Pull the Null Sensitivity switch down to the Low position and note that the null indicating meter needle moves to the right indicating too high a resistance setting
Download Pdf Manuals
Related Search