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Group 3 Digital Teslameters (Gaussmeters), DTM-133 & 151  


         DTM -151-G Manual - Revised July 2007 pdf, 185Kb
         DTM -151-S Manual - Revised July 2007 pdf, 482Kb
         DTM -133 with GPIB Interface Manual pdf, 4.1Mb
         DTM -133 with Serial Interface Manual pdf, 2.6Mb
         DTM -132 with GPIB Interface Manual pdf, 3.4Mb
         DTM -132 with Serial Interface Manual pdf, 2.7Mb
         DTM -130-G & DTM-141-G with GPIB & DTMG 5.0 Manual pdf, 1.4Mb
         DTM -130-G & DTM-141-G with GPIB & DTMG 4.1 Manual pdf, 3.1Mb


  Technical Notes

Using the DTM in high voltage or electrically noisy environments
   When using the DTM in electrically noisy environments, it is important to properly ground the instrument to protect it against high voltage transients. These transients can come from many sources, and could cause any number of problems ranging from overwriting the user and calibration tables, to actual physical damage to the DTM. We have prepaired a series of documents to guide in the proper installation and grounding of the DTM.

   PDF document: Fast Transient Immunity: Testing the Group3 DTM-151
                           to IEC1000-4-4
   PDF document: Fiber Optic Communications with Group3 DTMs
   PDF document: Installation Techniques for Electrically Noisy Environments
   PDF document: DTM Grounding Instructions

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Recovery when DTM tables are overwritten
   There are times when all the transient protection in the world just does not stop the random hit. If you are using the DTM with either of the computer interfaces, it is possible to detect and correct the error under automatic computer control, minimizing down time.  While this paper does not provide computer code, it does outline the steps required to make an automatic recovery.

   PDF document: Outline for automatic recovery of Calibration Tables

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Replacement of the DTM Firmware
   Periodically the firmware for DTM is revised, and it is often advantageous to upgrade the firmware. Here we have a list of the firmware revisions for all of the Group3 DTMs, and instructions on how to replace the EEPROM.  Do keep in mind that just because there is a new version, it is not necessary to upgrade.  The simple rule is: Only upgrade if you require it to fix a bug that may affect you, of if it offers a new feature that you desire.

   PDF document: Firmware replacement instructions

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My DTM displays the wrong field, over range, or overflow
   There are many reasons why a DTM may display a reading that is not what was expected. It could be in the wrong operating mode (AC vs DC), the 'users' modification table may have been changed, the calibration table may have been overwritten, or the probe or DTM has been damaged.  In most cases, and simple reset of the instrument will solve the problem.  

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What is the 'users' modification table?
   The users modification table is a series of values used to change the displayed field reading. These factors include filtering, zero, offset, scale, and others.

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Why would I not want the DTM to reset with power-on?
   If you have programmed a series of values in to the users modification table, or want to retain the zero point on the probe, you would not want the DTM to reset on power-on. The power-on reset would reset the table to it's default values, and you would then be forced to re-enter all of your user factors.

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How do I reset the DTM?
   The behavior of the power-on reset is controlled by a micro switch on the interface board in the DTM.  If the switch is in the 'off' position, no reset is executed during power-up.  If the switch is in the 'on' position, a reset is performed, and all the users factors are defaulted. 
   The instrument may also be reset over the computer interface by sending a CTRL-X charactor to the DTM.

   In all cases, the reset operation is confirmed on the DTM display with the message 'RESET'.

Please refer to the users manual for detailed information on the reset function.

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What causes the tables to be overwritten?
   This is generally caused by a voltage transient of high enough energy getting in to the DTM, upsetting the CPU. The CPU may then write random data in to the users modification table, and on rare occasions in to the calibration table itself.

   The best way to avoid or reduce the danger of this is to install a ferrite kit, use the Power Supply, Fiber Optic interface, and make sure the DTM is correctly grounded and shielded.

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When communicating with the DTM, after a short time it displays 'Group3'
   This is caused by polling the instrument too quickly and overflowing the DTM's recieve buffer.  It can occur in DTMs with either the IEEE-488 or RS-232 interfaces. The solution is simple, introduce a delay loop in the software to slow the polling rate.

   Remember that the DTM-133 updates the reading 30 times a second, and the DTM-151 updates at 10 times a second. Polling any faster than this will do nothing for you.

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The DTM displays 'Group3' all the time
   This is most often caused by the failure of the serial controller chip in the DTM. When th
e chip fails, it sends random charactors to the receive buffer at it's maximum data rate, overflowing the buffer, and causing a reboot. Note that this fault may occur even if you are not using the interface.

   The DTM should be returned for repair.

This page was last updated on 19 July, 2018
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