The document discusses monitoring energy consumption during electrical discharge machining. It proposes an electronic circuit using a microcontroller and analog front-end device to measure voltage, current and power parameters. The circuit can calculate active power, energy, total harmonic distortion and other metrics. It communicates measurements over CAN-bus to allow monitoring total energy usage and analyzing consumption patterns for different machine components.

1. Nonconventional Technologies Review 2012 Romanian Association of Nonconventional Technologies
Romania, June, 2012
SOME WAY TO MONITORING THE CONSUMED ENERGY, LOCAL AND
GLOBAL, DURING THE ELECTRICAL DISCHARGE MACHINING PROCESS
Emanoil Toma1, Carmen Simion2, Ioan P. Mihu3 and Mihail Aurel Ţîţu4
1
“Lucian Blaga” University of Sibiu-Romania, Department of Computers and Electrical Engineering, emanoil.toma@ulbsibiu.ro
2
“Lucian Blaga” University of Sibiu, Department of Industrial Engineering and Management, carmen.simion@ulbsibiu.ro
3
“Lucian Blaga” University of Sibiu-Romania, Department of Computers and Electrical Engineering, ioan.p.mihu@ulbsibiu.ro
4
“Lucian Blaga” University of Sibiu, Department of Industrial Engineering and Management, mihail.titu@ulbsibiu.ro
ABSTRACT:. The consumed energy is determined by sensing and processing the voltage and the current in front of the principal
consumers : the power supply of pulse generator, the displacement system of the electrode-tool, the x-y or other axis displacement
systems, the circulating system of dielectric liquid, eventually in front of the auxiliary activating systems (magnetic, ultrasonic). An
electronic circuit was conceived, based on the high performance microcontroller and dedicated Analogue Front End Device, in two
variants. The first variant is very simple; microcontroller receives one pulse at every watt-hour of consumed energy, accumulates it,
and communicates via CAN-bus. The second variant is more complicated in the software area; it can measure all power parameters:
W, VA, VAR, power factor, RMS voltage and current, total harmonic distortion. It can be a veritable energy analyzer if the software
is very elaborated. The main system can communicate with each measuring system and can offer a detailed evolution of consumed
energy for analysis.
KEY WORDS: Active Power, Energy, Analogue Front End Device, Microcontroller, Controller Area Network (CAN).
1. INTRODUCTION N=prop.W
For reducing the consumed energy in Electrical Discharge ELECTRONIC VOLTAGE
Machining (EDM) is necessary to monitor the consumed POWER TO-FREQUENCY
METER
energy for the entire machine tool and for the local consumers: I U
CONVERTER COUNTER
the power supply of pulse generator, the displacement system
LINE_IN LINE_OUT
of the electrode-tool, the x-y or other axis displacement
systems, the circulating system of dielectric liquid, eventually
in front of the auxiliary activating systems (magnetic, NULL_IN NULL_OUT
ultrasonic). The system can be applied for other dimensional
machining process. Figure 2. The principle of measuring schema
1.1. Energy measurement principle. The block diagram has a power meter, and the counter share
having a voltage to frequency converter and an electronic or
Electrical energy is defined by equation (1), referred to the electromechanical counter.
figure 1, where i is the instantaneous current, u is the
instantaneous voltage across the circuit and p is the Energy measurement could be implemented in two principal
instantaneous power. ways: analogue and digital.
e(t ) = ∫ p ⋅ dt = ∫ u ⋅ i ⋅ dt
(1) LINE_IN LINE_OUT
R1
i LOW
ux ANALOGUE
PASS
ELECTRICAL MULTIPLIER
FILTER
CIRCUIT u
R2
N=prop.W
VOLTAGE
TO-FREQUENCY
Figure 1. The energy defining schema CONVERTER COUNTER
If the power and the energy have positive sign the circuit is uy
Load and consumes energy. If the power and the energy have R_sense
negative sign the circuit is Source and delivery energy. The NULL_IN NULL_OUT
measuring circuit is must to sensing the current and the
voltage. The conditioning signals are must be multiplied. The
Figure 3. Analogue variant of energy measurement
results is must be integrated.
In the analogue variant, presented in the figure 3, the power
Measurement principle is illustrated in figure 2.
meter is based on an analogue multiplier.
53

2. On the inputs of the multiplier come two voltages. One is b0
proportional to the voltage line and the other is proportional to
the current. x[ n ] w[ n ] y[ n ]
Between voltage and current there are phase shifting (φ).
u (t ) = 2 ⋅ U ⋅ sin ωt (2) z-1 z-1
b1 a1
i (t ) = 2 ⋅ I ⋅ sin(ωt − ϕ ) (3)
y[ n-1 ]
U and I are the RMS (Root Mean Square) value of voltage and
current.
Figure 5. The diagram of digital Low Pass Filter (Infinite
The output of multiplier gives a voltage proportional to the Impulse Response Filter).
instantaneous power. The expression of is:
1.2. Actual state of energy measurements
p(t ) = u (t ) ⋅ i(t ) (4) techniques.
p(t ) = U ⋅ I ⋅ cosϕ − U ⋅ I ⋅ cos(2ωt − ϕ ) (5) Thanks to progress in technology of integrated circuits were
achieved complex circuits having inside analogue and digital
The instantaneous power has two spectral components: blocks like microcontrollers. Actually most measuring
The first term of (5) equation is average value, named real instruments are performed around a microcontroller. The
power. importance of energy for human society imposed achievement
the second term is an 2f harmonic component of many instruments for measuring electrical energy consumed.
The low pass filter must reject the 2f component. On the market there are portable measuring instruments named
electrical power analyzers. These instruments offer a lot of
The voltage to frequency converter produces the output pulses information about the quality of consumed energy:
proportional to the average real power.
catch power quality events such as fast transients
These pulses will be accumulated in electronic / (impulses) to few µs, voltage sags (dips), and swells;
electromechanical counter. track total harmonic distortion to the few tens harmonic;
The digital variant is presented in the figure 4: record energy use (kWh), and log all power parameters:
watts, va, var, power factor, etc.;
LINE_IN LINE_OUT
data log RMS voltage and current over time
(days/weeks/months) with cycle-by-cycle resolution;
R1 S&H
ANALOG
display real time values in meter window – just like a
TO-DIGITAL multimeter;
ux CONVERTER display oscilloscope waveforms, harmonic spectra, phasors
via a PC.
S&H These instruments also have one or more communications
ANALOG
modules, even wireless.
TO-DIGITAL
CONVERTER Having current and voltage probes, these instruments can be
R2 easy connected (see figure 6).
uy
NULL_IN
R_sense
NULL_OUT
current probe
L1
L2
N=prop.W MAINS L3 LOAD
DIGITAL
N
DIGITAL
LOW-PASS TO-FREQUENCY
FILTER CONVERTER COUNTER
ELECTRICAL
Figure 4. Digital variant of energy measurement ENERGY
The analogue signals ux and uy proportional of the voltage and ANALYZER
the current must be applied to the inputs of the sample and hold
dual unit. The two analog to digital converters furnishes
simultaneously at its outputs the two signals in digital form.
Figure 6. The connection schema of portable energy analyzer
The multiplier is hardware implemented for increase the speed.
In the consumed energy monitoring we can also use the energy
The digital low pass filter is usually a recursive filter based on
counters. These can be connected in circuit like in figure 7.
the structure showed in figure 5 [4].
54

3. Programmable gain amplifier (PGA) can be programmed to
have 1, 2, 4 or 16 gain factor, according to the value of
R_sense. Analog to digital converter is 16 bits delta-sigma
L1 L1_IN type. Two digital high-pass filters cancel the system offset on
L2 ENERGY L1_OUT both channels such that the real-power calculation does not
L2_IN L2_OUT
MAINS L3 COUNTER L3_OUT LOAD include any circuit or system offset.
L3_IN
N N_IN N_OUT
After being high-pass filtered, the voltage and current signals
are multiplied to give the instantaneous power signal. This
signal does not contain the DC offset components, such that the
averaging technique can be efficiently used to give the desired
active-power output. The instantaneous power signal contains
Figure 7. The connection schema of energy counter the real power information; it is the DC component of the
instantaneous power. The averaging technique can be used
It is obvious the necessity of inserting the energy counter in
circuit between mains and consumer. Between line_in and with both sinusoidal and non-sinusoidal waveforms, as well as
line_out there are a shunt resistor or primary coil of current for all power factors. The instantaneous power is thus low-pass
transformer. If the current transducer is based on Hall Effect, filtered in order to produce the instantaneous real-power signal.
between mains and load there are only a wire [1], [2], [5]. A digital-to-frequency converter accumulates the
instantaneous active real power information to produce output
2. MODULES OF ENERGY MEASURING pulses with a frequency proportional to the average real power.
BASED ON MICROCONTROLLER AND The low-frequency pulses present at the FOUT0 and FOUT1
ANALOG FRONT END CIRCUIT outputs are designed to drive electromechanical counters and
two-phase stepper motors displaying the real-power energy
According to the necessity of reducing power consumed in
consumed. Each pulse corresponds to a fixed quantity of real
electrical discharge machining, we conceived a low cost
energy, selected by the F2, F1 and F0 logic settings.
module, to be placed in front of each share part consumer of
the machine tool (the power supply of pulse generator, the The pulses are applied to timer input of microcontroller. The
displacement system of the electrode-tool, the x-y displacement microprocessor substitutes the electronic/electromechanical
system, the circulating system of dielectric liquid, eventually in counter and supplementary communicates on industrial CAN
front of the auxiliary systems (magnetic, ultrasonic)). bus with other modules and/or PC.
The simplified electrical schema is showed in figure 8. Optionally the module can also communicate with PC via
RS232 serial interface.
We used for current sensing a shunt resistor (R_sense)
followed by a programmable amplifier contained in the Analog For three phase energy counter is necessary to have three
Front End (AFE) circuit MCP3905. The power supply for the analog front end circuits MCP3905, like is showed in figure 9.
AFE circuit, showed in figure 10, is referred to the LINE_IN
Every AFE circuits have proper power supply referred to the
point.
own LINE_IN point and proper voltage and current sensing
For voltage sensing we used a voltage divider (R1, R2). circuits also. On the other hand every AFE circuits have is
Maximum voltage applied to the input of amplifier is a few followed by proper opto - coupler circuit to transmit pulses to
mV. microcontroller.
LINE_IN R_sense LINE_OUT
VDD1 VDD1 VDD_AUX
AVDD DVDD
ANALOG DIGITAL VDD
CH0+ CAN- TRANSCEIVER
R2 +
1
C1TX TX CAN H 2
CH0-
- VDD_AUX
C1RX RX CAN L
3
MICROCONTROLLER
PGA ADC HPF i FOUT0
16-Bit
p FOUT1 R4
U2
HFOUT R3
IC2
u 1
LPF DFC 6
2
CH1+ U1RX
RS232
+ TCDT1101G
3
7
U1TX 8
4
CH1-
- 5
9
A ADC MCP3905
DB9_F
HPF VSS
AVSS DVSS
R1
NULL_IN NULL_OUT
Figure 8. The simplified electrical schema of proposed energy measuring module
55

4. R_IN R_sense_R R_OUT R_sense
VDD_R VDD_R VDD_AUX
LINE_IN LINE_OUT
VDD_AUX
U1 VDD
CH0+
AVDD DVDD
R4
CAN- TRANSCEIVER C19 100n
1
C1TX TX CAN H
R2_R
VDD_AUX
2
U4
R3 3
CH0-
HFOUT
C1RX RX CAN L
IC1
MICROCONTROLLER
CH1+
C18 10u/16V
16-Bit
MCP3905
CH1-
IC2
AVSS DVSS
1
6
2
U1RX
RS232 7
1
2
3
4
3
U1TX 8
IC3 4
9
5
DB9_F U6 78L05
VSS
8
7
6
5
S_IN R_sense_S S_OUT
VDD_S VDD_S
VDD_AUX
U2
C17 2U2
AVDD DVDD
CH0+ R6
R2_S U5
R5
CH0-
HFOUT
CH1+
4
3
MCP3905
CH1-
AVSS DVSS
U5 0
AM1D-1212
T_IN R_sense_T T_OUT
1
2
VDD_T VDD_T
U3
VDD_AUX
C16 470u/16V
AVDD DVDD
CH0+ R8
R2_T U6
R7
CH0-
HFOUT
D3
CH1+
MCP3905
CH1-
AVSS DVSS 1N4007 D2 PL15Z
C15
R1_R R1_S R1_T
470nF/630V RV1 275V
NULL_IN NULL_OUT
Figure 9. The simplified electrical schema of proposed three R15
phase energy counter 470/2W
NULL_IN NULL_OUT
R_sense
LINE_IN LINE_OUT
Figure 11. Electrical schema of microcontroller and
VDD1
communication port power supply
C23 100n
Analog Front End device used in fig. 8 is MCP3905 and
another version, like MCP3909, has supplementary a digital
serial peripheral interface and can communicates with
microcontroller.
1
2
3
4
The microcontroller read the value of instantaneous real
U7
power and calculates the energy.
78L05
The microcontroller can read the value of voltage and
instantaneous current for calculating the RMS value, Fourier
8
7
6
5
transforming, total harmonic distortions, etc.
C21 470u/16V
CAN_BUS
MODUL
D5
no_2
MODUL
1N4007 D4 PL15Z
no_1
C20
MODUL
470nF/630V RV2 275V MODUL
no_3
no_k
R17
470/2W
NULL_IN NULL_OUT CAN_ADAPTER
Figure 10. Electrical schema of AFE power supply PC
Power supply for microcontroller and CAN transceiver must be Figure 12. Connection diagram of the modules
galvanic separated toward mains. We used an integrated DC to
DC converter AM1D-1212 (figure 11). Both power supply offer
a weak current. If the microcontroller is used to perform more
calculus the consumed current increase. In this case another
schema of power supply is necessary.
56

5. R_sense
LINE_IN LINE_OUT
AVDD DVDD
U4
ANALOG DIGITAL
VDD1 VDD2
R2 VDD
CH0+
+ + + SINC 3 CAN- TRANSCEIVER
OSC1
PGA OC1
-
1
CH0- ADC FILTER DR C1TX TX CAN H
- - RB2
2
3
SDO C1RX RX CAN L
SDI
MICROCONTROLLER
VSS1 VSS2
DIGITAL 0
16-Bit
PHASE SPI
SHIFTER RESET
RE0
INTERFACE SDI
VDD1 VDD2 SDO
SCK 1
SCK 6
CH1+ CS
+ + + RE1 U1RX
2
SINC 3 MDAT0 RS232 3
7
PGA RB3 U1TX
-
8
CH1- ADC MDAT1
- - FILTER RB4
4
9
5
VSS
VSS1 VSS2 DB9_F
0
AVSS DVSS
R1
0 0
NULL_IN NULL_OUT
Figure 13. The simplified electrical schema of proposed energy analyzer module.
performed by precedent AFE: digital multiplication, the offset
The Analog Front End device used in figure 13 communicates
rejection, and low-pass filtering. Moreover, an adequate
with microcontroller through the digital serial peripheral interface
software implemented on microcontroller could offer the
(SPI). AFE not includes digital multiplier and digital low pass-
possibilities to measure another parameters like RMS value of
filter. It offers information about only instantaneous value of
voltage and current, active power, apparent power, power
current and voltage.
factor such as is showed in figure 14.
The 24 bits delta-sigma ADC increases the accuracy of
measurement. The microcontroller must achieve the functions
Figure 14. The diagram of power parameters digital calculation.
4. Mateescu, A., Dumitriu, N., Stanciu L. Semnale şi sisteme
3. REFERENCES – Aplicaţii în filtrarea semnalelor, Editura Teora, ISBN
1. King, C., IEC Compliant Active-Energy Meter Design 973-20-0666-8, Bucureşti, (2001).
Using The MCP3905A/06A, Available from: 5. Moulin, E. Measuring Harmonic Energy with a Solid
http://ww1.microchip.com/downloads/en/AppNotes/00994 State Energy Meter, Available from:
b.pdf http://www.analog.com/static/importedfiles/tech_articles/1
2. King, C., Quiquempoix, V. Designing with the MCP3901 7011149511795ANALOG_PAGE_68-71.pdf
Dual Channel Analog-to-Digital Converters, Available 6. Toma, E., Mihu, P. I., Nanu, D. Some possibilities to
from: monitoring the energy consumed in electrical discharge
http://ww1.microchip.com/downloads/en/AppNotes/01300 machining, Proceedings of the 15th International
a.pdf Conference, Modern Technology, Quality and Innovation,
3. Chlebis, P., Pumr, J., Simonik, P. Current sensor with the Vol. II, pp 1077-1080, Vadul lui Voda-Chisinau, Republic
DSP, International Conference, Applied Electronics (AE), of Moldova, (2011).
ISBN: 978-80-7043-865-7, (2010).
57