Single channel resistivity meters with automated electrode switching options.
The Syscal Junior and R1+ models are single channel resistivity meters that may be used in a traditional four electrode approach, or may optionally be extended to automated switching type (resistivity imaging systems). If you are looking for only the most basic of resistivity meters please go to www.geo-resistivity.com. If you are interested in the most advanced multi channel type resistivity meters then please go to www.resistivitymeter.com.
The Syscal Junior and Syscal R1+ resistivity meters are more or less identical designs, except for the amount of transmitting power. The Syscal Junior offers a maximum 400Volt(800V peak to peak) transmitting pulse, at maximum 1.2A, and maximum 100Watt. The Syscal R1+ offers 600V(1,200V peak to peak), 2.5A, and 200W.
Both resistivity meters feature a two channel design, allowing simultaneous measurement of both voltage and current. Syscal resistivity meters are the only systems that incorporate this method of resistivity measurement. This permits the most accurate resolution of signal, and greatly facilitates rejection of unwanted noise.
Much attention is often given to the lowest possible voltage measurement that can be made by an instrument. This is somehow felt to indicate the sensitivity of one design over another. Yet, this number is often quite misleading. Syscal meters all use a 20 bit converter. With any analog to digital converter(A/D) there will be some noise in the hardware itself. Some manufacturers attempt to amplify a very small signal buried in the A/D noise and report this as the theoretical sensitivity of the instrument. Rather than try to create a specification that is meaningless you will see the Syscal meters claim a very attainable 1 microvolt sensitivity.
The real issue is to be able to measure a signal that is above the noise of the A/D. This signal must be well above the noise of other artifacts of the measurement process, such as spikes in the SP value. These spikes are always present and may not be removed completely even by linear drift correction. This is why Syscal instruments offer a range of transmitting power, so that you can use an instrument with sufficient power for your typical survey and measure a signal significantly above the noise level.
During the stacking process a sophisticated algorithm is running, correcting for the SP drift, and filtering the data, removing noise spikes that are outside typical ranges. Syscal instruments are known for their excellent results in noisy conditions, and this algorithm deserves much of the credit for this result. All Syscal instruments allow the operator to set a minimum number of stacks, a maximum number of stacks, and a standard deviation such that when this quality level is reached the stacking process is stopped. This permits surveys to be done in a timely and efficient manner, while retaining the quality of results desired.
If you are considering a multi electrode sampling system for your meter then the design of the Syscal Switch system will be of interest. The Switch designation is used for meters that have been fitted with electronic switches, to allow automatic sampling through a set of electrodes. In the early versions of multi electrode systems manufacturers placed the electronics for switching out on the cable at each electrode position. Over time it became apparent that this was a less than ideal solution, as the nodes received a lot of wear and tear on the cable, and the cost to manufacture individual nodes was high. A better solution was found by putting the switches in the meter. Manufacturing cost was reduced and a much more robust cable was the result. Today the Syscal Switch type meters use a multiconductor cable, designed by a company that has been making such cables for more than twenty years. The cables are reliable, lighter in weight than the previous generation, and more easily field repaired if ever required.
A profile is collected by setting up the instrument with all 24(or more) electrodes and collecting the array desired. The profile line is extended by then moving the instrument to the end of the first line(electrodes 13-24), and the first cable section(electrodes 1-12) is rolled forward in front of this. This is much the same method as used for seismic data collection. Since the cables are double ended there is no need to move the second cable section. The resistivity instruments are preprogrammed for the new array for a roll along so that only the new electrode positions are sampled in the next measurement sequence.
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Depth capability for any resistivity meter is a very difficult number to suggest, as it is highly dependant on geology, and how much stacking time an operator is willing to invest. For the Syscal Junior we feel a depth of 100m is a conservative value that should be possible in all but the most difficult locations. For the Syscal R1+ the depth is extended to 200m. For the Switch type systems depth is limited by the profile length. With an electrode spacing of 5m and 48 electrodes, yielding a profile length of 240m, a survey depth of 48m would be typical.
The Switch versions of the Syscal Junior or Syscal R1+ are offered in configurations of 24, 48, or 72 nodes. These would be designated as models Syscal Junior S24, Syscal Junior S48, or Syscal Junior S72. Standard spacing on any Switch type system is 5m, and may be optionally specified at any spacing up to 10m. Typical survey depth capability for a 72 node system at 5m intervals is 70m(360m profile length).
Creation of the array to be sampled with multi electrode systems used to be time consuming and difficult. This problem was addressed with the release of the Electre II software. The user friendly interface allows the user to see the array as it is designed, with electrode position, depth, and total number of readings required. Electre II will automatically generate a full sequence of "a" spacings, such as "2a", "3a", etc. As these are selected the operator can see the expected depth, and the lateral and vertical density of data points. Once an array is designed Electre II permits the generation of a roll along sequence corresponding to this array with only the added readings required.
This section represents the position of each plotting point for a sequence of measurements. The section has been interactively defined by the operator to include the following parameters:
|-Cable Definition: cable shall consist of two sections, each with 24 electrodes at 5m spacing|
|-Electrode Array: Wenner-Schlumberger|
|-First Electrode Spacing: a=5m;||Depth Levels n(a)=1, 2, 3, 4, 5, 6 ||Green Dots|
|-Second Electrode Spacing: 2a=10m; ||Depth Levels n(2a)=3, 7/2, 4 || Yellow Dots|
|-Third Electrode Spacing: 3a=15m;||Depth Levels n(3a)=8/3, 3, 10/3 || Blue Dots|
At each step of introducing these parameters the operator can make changes and see in real time the effect this will have on the section. The horizontal axis indicates the profile length for a cable of two sections of 24 electrodes at 5m spacing. The vertical scale is the plotting depth in meters, as defined by Edwards and Loke. In this case the maximum depth for this sequence is 22m. The total number of readings is indicated in the upper right corner as 417 readings. This entire sequence will be completed with an acquisition time of about forty minutes, based on a typical number of stacks per reading of 5, and a pulse duration of 0.5 seconds.
After data collection and transfer back to a PC the ProSys software package allows further data processing capabilities. The user may edit the data set and remove erroneous data manually, or automatically by entering a specified criteria, such as data points exceeding a certain standard deviation. The final data file is formatted for the popular 2D and 3D interpretation software packages such as Res2D/3DInv.
A second option offered with these resistivity meters is the Switch Plus external switching box. We can put a maximum of 72 nodes into the case of either a Syscal Junior or R1+. For users who want to go to greater than 72 electrodes, particularly for 3D surveys, we connect one or more Switch Plus Boxes which typically will contain 24-72 nodes. These boxes may be spaced a maximum distance of 20m from the resistivity meter itself and each other. As illustrated below this concept allows rolling along the line, or down the line, with several hundred electrodes.
Two types of line layouts are possible, as shown to the left and below. At the left are shown eight lines of 24 electrodes each, with the system set to roll to additional lines.
Here we show the ability of the system to roll along the line, running 4 sets of 48 electrodes per line. For practical ease the recommended array is a combination of in-line colinear dipole-dipole, and broadside equatorial dipole-dipole, the latter having a greater depth of investigation.