FIELD OF THE INVENTION
The present invention generally relates to a "Welding Power source Digital read
out Calibration equipment". More particularly the invention relates to a device for
direct verification of digital read outs of current and voltage in a welding power
source.
BACKGROUND OF THE INVENTION
In fabrication industries, Welding plays a major role in the manufacturing
process. The high current required for welding is provided by Welding power
sources. Read out mechanisms are incorporated in the welding power sources
for measuring the welding current and Voltage parameters.
The Quality of the weld ments is directly related to said welding parameters and
hence, the readout mechanisms in these power sources need to be verified /
calibrated on periodical basis to ensure that the process parameters always
remain within allowable tolerance values.
a)In traditional welding power sources, the ammeters and voltmeters are the
detachable units and they can be removed separately. For calibrations, test
voltages are applied to these meters through a standard reference source. The
calibration through this method is a simpler process and normally takes a
maximum of 5 to 10 minutes per instrument.

b) In the technologically advanced welding power sources, the ammeters
and voltmeters are replaced with digital read outs which are directly
integrated to a Micro processor Printed Circuit Boards (PCB). These
readouts have provided a greater compactness to the welding power
sources. Apart from that, these readouts are also used for the display of
Error code messages and used to set the process parameter values.
These digital read outs cannot be removed from the units and hence cannot be
calibrated as like the ammeters and voltmeter in traditional welding machines.
Hence calibration of these read outs has become a complicated process.
Verification of the process parameters of these latest technology welding power
sources is known to have been carried out in a complex method, wherein the
output leads from the current measurement shunt and the welding terminal
voltage measurement wires which are connected to the micro processor have to
be traced out amidst the bunch of the wires and needs to be verified with a
reference standard. In case, a wrong wire is disconnected, then the entire welding
machine gets tripped as the signals through the cables are used for other control
process also.
Therefore, according to the known method, a verification has to be done only
when the machine is powered on which adds to a Safety hazard also. Further, this
method is extremely time consuming and may require 4 to 5 hours for the
calibration of a single power source. Also, at least three man power is required for
this known method as the entire process involves disassembly of the welding
power source, tracing the signal cables and calibration activities.

OBJECT OF THE INVENTION
It is therefore an object of the invention to propose a device for direct verification
of digital read outs of current and voltage in a welding power source.
These and other objects and advantages of the invention will be apparent from the
ensuing description.
SUMMAY OF THE INVENTION
In a first aspect of the invention, there is provided a device for. direct verification
of
welding power source, digital read outs of current and voltage in the device
comprising a power input module (1) having a Step down transformer (Tl), a
Bridge rectifier unit (BR), and a plurality of filter capacitors to provide a DC supply
to an electronics control circuit; at least one set of Voltage regulator (2) having a
first and a second Voltage regulator (VR1 and VR2) to regulate the DC supply
input for the control circuit; a measurement shunt (3) to measure the welding
current by the mV drop across the shunt; a digital Volt Meter for measurement of
terminal voltage of the device; a digital Ammeter (5) for measurement of welding
current; a Reference Shunt (6) to provide a reference voltage for the control
circuit ; a plurality of load bank switch over contactors (K1, K2, K2) (7) for load
bank selection;
a load Bank (8) consisting of a plurality of Resistors (R1, R2, R3, R4, R5 and R6),
an amplifier Circuit (9) for amplification of the mV reference voltage from the

reference shunt (6); an inverter circuit (10) for polarity changing; a comparator
circuit (11) for comparing the reference signal and the set reference value to
provide corresponding control output; a relay drive (12) for driving a relay which in
turn actuates the main contactors; and cooling means (13) for cooling the load
bank (8).
According to the methodology of the invention, the device is connected across the
Welding power source's output terminal. This equipment is provided with 2
numbers of Shunt (Measurement and Control circuit Reference purpose), a Load
bank arrangement, one each Digital Ammeter, and voltmeter (Reference
standard), Control PCBs, Cooling circuits and load bank switch over contactors.
Most of the known micro processor based welding machines requires a minimum
load current of 30 A for initial start up. The present invention provides a specific
method of establishing this load current through an innovative load bank
arrangement. During the initial start up, more resistance is required and for the
subsequent increase in current readings, the load resistance has to be decreased.
This is achieved through a Control circuit and the Load bank switch over
contactors. The control circuit employs a reference shunt which feeds the mV input
dropping across it to an operational amplifier. The operational amplifier in turn
amplifies the input signal and activates the relay which in turn will activate the
contactors.
The actuation of these contactors make the load resistances to combine in parallel
manner and decrease the cumulative load resistance value.

The welding current is made to pass through the measurement shunt and the mV
drop across it, is used for the current measurement. The voltage across the
welding terminal is measured by the standard voltmeter.
Since, a large amount of current is flowing though the load bank, a cooling
mechanism is also inbuilt to the unit for safety purpose.
BRIEF DESCIPTION OF THE ACCOMPANYING DRAWING
Figure 1 shows an Electrical Schematic diagram for the 'Welding Power source
Digital read out Calibration equipment".
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
As shown in figure 1 "Welding Power source Digital read out Calibration
equipment" consists of a Power input module (1): which comprises of Step down
transformer (T1), Bridge rectifier unit (BR) and Filter capacitors. It is to provide a
DC supply to the electronics control circuit.
Voltage regulators (2): Which comprises of Voltage regulator VR1 and VR2 which
will regulate the DC supply input for the control circuit.
Measurement shunt Sh1 (3): used to measure the welding current by using the
mV drop across it.
Digital Volt Meter - DVM (4): Used for the measurement of terminal voltage.

Digital Ammeter - DAM (5): Used for the measurement of welding current through
Sh1 (3).
Reference Shunt Sh2 (6): Which will provide the reference voltage for the control
circuit.
Load bank switch over contactors - K1, K2 and K3 (7): Used for load bank
selection.
Load Bank (8): Consists of resistors R1, R2, R3, R4, R5 and R6 used for varying
welding current
Amplifier circuit (9): Used for the amplification of the mV reference voltage from
Sh2.(6)
Inverter circuit (10): Used for polarity changing
Comparator circuit (11): Used for comparing the reference signal and the set
reference value and will provide suitable control output.
Relay drive (12) : Used for driving the relay which in turn will actuate the main
contactors.
Cooling system (13): used for cooling the Load bank
The output leads of the welding machine whose digital read outs needs to be
calibrated, has to be connected to the Calibration equipment's calibration terminal

by means of connecting cables. By doing so, Calibration equipment's Measurement
shut Sh1 (3) and the reference shunt Sh2 (6) are connected in series with the
negative terminal of the winding machine. The other end of the reference shunt
Sh2 (6) is getting connected to the positive terminal of the welding machine
through the Load bank arrangement (With high resistance mode in place) (8). The
welding current is measured through the Digital ammeter (5) which is connected
across the Measurement shunt Sh1 (3). The welding voltage is measured through
the Digital voltmeter (4) which is connected across the welding machine's output
terminal.
This initial start up will be used for the measurement of currents and voltages upto
a certain level only. For measuring higher currents, the resistance provided by the
load bank needs to be decreased which is being carried out by the innovative Load
bank switch over mechanism.
This mechanism consists of a Reference Shunt Sh2 (6) which is connected to
series with sh1 (3). The mV drop across sh2 (6) will be given a input to the
amplifier circuit (9). The polarity changing of the output from (9) is achieved with
a Inverter circuit (10). The output from inverter circuit (10) is fed to a comparator
circuit (11) The comparator makes a logical decision by comparing the input from
inverter circuit (10) and the preset reference value given to that. Based on the
logical decision, a relay driver circuit (12) is activated. This relay driver circuit (12)
will in turn actuate the Contactors K1, K2 and K3 (7) will in turn after the
resistance combination arrangement by paralleling the resistance and will decrease
the load resistance.
Since, lot of heat is dissipated through the load bank (8) due to higher current
flow, a cooling mechanism (13) is incorporated for Safety purpose.

WE CLAIM :
1. A device for direct verification of welding power source, digital read outs
of current and voltage in the device comprising :
- a power input module (1) having a Step down transformer (T1), a Bridge rectifier
unit (BR), and
- a plurality of filter capacitors to provide a DC supply to an electronics control
circuit;
- at least one set of Voltage regulator (2) having a first and a second Voltage
regulator (VR1 and VR2) to regulate the DC supply input for the control circuit;
- a measurement shunt (3) to measure the welding current by the mV drop across
the shunt;
- a digital Volt Meter (4) for measurement of terminal voltage of the device;
- a digital Ammeter (5) for measurement of welding current;
- a Reference Shunt (6) to provide a reference voltage for the control circuit;
- a plurality of load bank switch over contactors (K1, K2, K2 (7) for load bank
selection;

- a load Bank (8) consisting of a plurality of Resistors (R1, R2, R3, R4, R5 and
R6),
- an amplifier Circuit (9) for amplification of the mV reference voltage from the
reference shunt (6);
- an inverter circuit (10) for polarity changing;
- a comparator circuit (11) for comparing the reference signal and the set
reference value to provide corresponding control output;
- a relay drive (12) for driving a relay which in turn actuates the main
contactors; and
- cooling system means (13) for cooling the load bank (8).