Teslameter - Gaussmeter
Digital Magnetic Field Measurement Instruments
Group3 Teslameters offer: - Outstanding accuracy
- Extremely high resolution
- Small probe size
- Single probe covers all fields up to full scale.
- Noise immunity
- Interchangeable probes
Group3 teslameters are the highest precision Hall effect instruments available - no other instrument can offer comparable specifications in the same price range. Group3’s unique linearization and temperature correction techniques have overcome the inherent problems of standard Hall effect devices. Every Group3 probe is individually characterised at many hundred field values, each at a range of temperatures. All this data is analysed by the calibration computers and the resulting correction coefficients stored in the probe itself. Advanced software algorithms in a Group3 Teslameter use the data to produce corrected field readings.
No other instrument available approaches the thermal stability of the DTM-151 and LPT-141 combination - conservatively rated at 10ppm/° C maximum, but typically less than half of that.
The small active area of a Hall probe is ideal for field mapping. It offers particular advantages in regions of non-uniform field, for making measurements "on-the-fly" (when moving the probe through a field region), and also for measuring AC magnetic fields. These are applications where NMR based teslameters do not operate well. The high precision Group3 teslameters offer near equal resolution, can operate in all these difficult areas, and cost far less than an NMR system.
Because the characterisation data for each probe is permanently stored within the probe plug housing itself, any Group3 probe can be used with any Group3 instrument. Probes and instruments can be swapped around while still maintaining the full accuracy of the system.
A single probe covers a wide range of field values - there is no requirement to change probes.
A selection of probes is available, of differing areas, sensitivities, and temperature dependence.
The Group3 instruments are robustly housed in an all metal case, which also gives added protection against RFI problems. The small sized unit takes up little space on a benchtop, and if the panel mount version is used, three teslameters can be mounted across a standard 19" panel.
The field reading is on a 7 digit red LED display, highly visible in the normal laboratory environment, and particularly good if the unit is installed in some poorly lit area.
The front panel is kept simple, with just two buttons needed to select and change settings. Group3 has adopted this elegant approach, rather than providing a button for everything, whether its required or not.
The sophisticated drive methods employed, and the very special cable used for the probes permit large separations of probe head and instrument. Probe cables can be manufactured up to 30 metres in length.
Group3 offers three distinct families of teslameters
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High precision DTM-151 series - the premium Hall effect teslameter.
- outstanding accuracy, very high resolution (1 in 600,000)
- for use with temperature compensated probes.
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High resolution DTM-150 series
- same high resolution as the DTM-151
- for use with non-temperature compensated probes.
- Same accuracy as DTM-151 at room temperature (25° C) Intended for use where the probe will be held at a constant temperature, or where the full accuracy over temperature is not required.
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Economy DTM-133 series.
- lower resolution, (1 in 12,000 )
- For use with non temperature compensated probes
The basic instrument of each series then has a number of options that can be added:
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communications
- options of either serial - ( RS232 and fiber optic) or IEEE488 / GPIB
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mounting
- bench instrument or rack panel mount.
Be careful when making comparisons based on other manufacturers’ specification sheets.
Group3 has always quoted an overall accuracy specification, for the full system - instrument plus probe, over the quoted field and temperature range. After all, it is the system accuracy that is of interest to someone doing the measurement - a probe or an instrument alone is of little use.
Frequently other manufacturers will quote a spec. for the instrument, another for the probe, and another for the temperature dependence of the probe. While all these individual numbers may look small, to get the system performance, you need to add all the inaccuracies together. Remember that a probe quoted with a number like 0.02% / ° C may initially look good, but when you multiply it by the 50° C operation range that is standard of a Group3 probe, all of a sudden the competing probe is actually a 1% device.
Another ploy of some other manufacturers is to claim that "absolute accuracy" is a difficult specification to give, and prefer instead to quote "precision or repeatability". First of all, absolute accuracy is easy to quote for a teslameter system - all you have to do is ask "how accurate is the reading, when compared to a known standard?" An NMR probe is generally accepted as the best reference standard, and Group3 probes are checked for absolute accuracy against an NMR meter. The Group3 DTM-151 teslameter systems can be reliably quoted at an accuracy of 0.01%, considerably better than other teslameters.
Secondly, precision or repeatability are meaningless terms unless obtained under absolutely defined conditions, which don’t really occur in real measurement situations.
The two prime specifications should be Absolute Accuracy (when compared to a known standard), and Resolution ("what is the smallest change in field that the instrument will detect?")
Teslameter Selection Guide
Ordering Information
DTM-151 and DTM-150
Available as standard with either serial communications or IEEE488 bus communications.
Available as free standing bench instrument, or with a panel mount bezel.
| Model | Details |
|---|---|
| DTM-150-DS | bench instrument, RS232 comms. |
| DTM-150-DG | bench instrument, GPIB / IEEE488 comms. |
| DTM-150-PS | panel mount, RS232 comms. |
| DTM-150-PG | panel mount, GPIB / IEEE488 comms. |
| DTM-151-DS | bench instrument, RS232 comms. |
| DTM-151-DG | bench instrument, GPIB / IEEE488 comms. |
| DTM-151-PS | panel mount, RS232 comms. |
| DTM-151-PG | panel mount, GPIB / IEEE488 comms. |
DTM-133
Available as standard without any communications.
If required, specify either serial communications or IEEE488 bus communications.
Available as free standing bench instrument, or with a panel mount bezel.
| Model | Details |
|---|---|
| DTM-133- D | stand alone, no comms |
| DTM-133- P | panel mount, no comms |
| DTM-133- DS | stand alone, serial comms |
| DTM-133- PS | panel mount, serial comms |
| DTM-133- DG | stand alone, GPIB/IEEE488 comms |
| DTM-133- PG | panel mount, GPIB/IEEE488 comms |