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MI Sensor Welding Machine
MI-Welder1

The TRM MI sensor welding machine is designed specifically to weld the Measuring (hot) junction of mineral insulated Thermocouples. The machine can also weld Pt100 sensors in MI constructions as wells as closing Stainless Steel tubes for Tube-and-wire sensor manufacture. TRM cannot accept responsibility for damage caused by using the machine outside this scope.
 
The TRM MI sensor Welding Machine will be of interest to all manufacturers of Metal Sheathed Thermocouples and Platinum Resistance thermometers, where its great versatility makes it suitable for both high volume production and short run 'Specials'.
 
DIMENSIONS
 
The maximum outside dimensions of the machine, including the Microscope and weld table are:
MI-Welder2
500mm wide
 450mm high
 755mm deep
 
The bench footprint is:
 
500mm wide
 480mm deep
 
CONSTRUCTION
 
The main case of the machine is constructed from 16 gauge Mild Steel, Epoxy powder coated on all inside and outside surfaces. The panels, which make up the case, are bolted together by M6 x 1.0 bolts into captive nuts.
The side panels have punched louvers to assist airflow through the internal components. Airflow is further assisted by means of internal fans.
Small sub-panels on the rear of the machine allow limited access to the main connections, fuses and to replace the light source for the fibre optic illuminator.
 
FUNCTIONS
 
The welding machine is designed to perform two separate operations and hence is divided into two sections with the following functions;

A) A capacitance discharge section designed to produce a short, high energy pulse to weld two small components together. This pulse is delivered to the components through a high voltage, high frequency spark which ionises an inert gas present at the weld site. The charge delivered can be varied by selecting the value of capacitance and by altering the charge voltage level. There are 10 capacitors connected in 5 parallel groups of 2. Each serial group of 2 can be selected individually until all 5 are in circuit. The capacitors are all 2200MFD 400v dc Electrolytics specially suited to energy discharge use, having low inductance and impedance values. The charge Voltage can be anything up to 600v dc.
 
MI-Welder3B) A TIG welding section designed to provide a lower energy, long duration cycle of a typical controlled profile (i.e. Slope-up, hold & slope-down). This section also uses high frequency starting and the same electrodes as that in 'A' above and is designed to operate with high stability at currents substantially lower than ordinary TIG welders.
 
An auxiliary secondary voltage is used to provide a high open circuit potential during arc starting and to supply charge current to the impulse starting capacitor. This is to ensure a clean but soft start even at low currents. The machine is designed to be compact by incorporating the minimum of electromagnetic components such as transformers and relays.
 
The machine requires a supply of High Purity Argon Gas. Use of any other Argon or Helium gas mixtures will alter the characteristics of the weld arc. Advice must be sought before using gases other than High Purity Argon.
 
OTHER FEATURES
 
Since the machine has an optional built in microscope and light source almost all of the operations involved in preparing and welding MI thermocouples can be carried out at the Machine.
 
Preparations for welding is achieved using small tools designed to remove the mineral insulation and prepare the internal conductors for welding.
 
The closure of the sheath is effected using optional compatible 'caps' designed to provide weld material to give a complete solid closure.
 
MI-Welder4Pre and post gas deployment means that the weld material stays clean with very much reduced oxidation. In particular, post-gas can be used to cool the weld without undue oxide built-up and in many cases the weld needs no further cleaning.
 
The vice holding the cable can slide out from under the weld torch to the focal point of the microscope. This makes it easy to re-examine the works as it progresses.
 
After the automatic weld sequence the perfect closure weld can be repeated over and over again with exactly the same settings under microprocessor control.
 
The TRM MI Sensor Welding Machine is designed to be stood on a bench to allow the operator to remain in a seated position for most of the operations involved in producing a thermocouple. This makes it easier for the operator and increases the productivity of thermocouple manufacture. It is recommended that the machine is installed in a semi-clean environment away from the heavier engineering aspects of a production facility. The room should be well lit and free from excess dust.
 
MI-Welder5Although specifically designed for welding MI Thermocouples the TRM MI Sensor Welding Machine has been used to great effect in the manufacture of Wire-in-tube sensors. The ability to reproduce the same weld parameters over and over again makes it the welder of choice for Sensor Production facilities Worldwide.
 
Every welder sold includes a comprehensive training manual which includes details for manufacturing MI thermocouples. In addition training can be given for all aspects of thermocouple manufacture.

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