p://rutex.com
)
1
Plasma torch height control system
for profile cutting machines
- control PCB.

Features:

- DC 24V output for standard brushed permanent magnet motor
- constant torch height control done by means of sampling the
arc voltage
- initial height sensing prior to cut
- adjustable gain and up/down speed
- single DC 24V supply
- PCB size 100 x 80 x 30 mm


General description:

The 953-00x control system is an interface between CNC controller or tracing head and Plasma unit. 953-
00x provides all necessary signals for controlling the up/down movement of the cutting torch.

Detailed description:
A switch mode servo driver drives the motor. For simplicity of interfacing the speed feedback (tacho,
encoder, etc.) has been omitted and the back EMF voltage from the winding of the motor is integrated and
used as a speed feedback for the driver. The driver can deliver close to 2 amperes peak current at nearly
100 % duty cycle. When the up (or down) input is activated, this connects the positive (or negative) supply to
input of the driver.
The arc voltage must be externally divided into less than 5 volts. This signal is applied to ARC_VOLTAGE_1
and _2. The difference between arc voltage and reference voltage is amplified and fed to the servo driver.
The speed of the movement is proportional to the difference of these voltages. The reference voltage is a
preset value of the arc voltage, 0 to +5V, delivered from panel mount potentiometer or analogue output from
the CNC.
The auto sequence logics are used for the initial height sensing. When enabled (+AUTO) and +PLASMA
signal is toggled on (from manual START switch or CNC controller), the torch is lowered down, the
+24V_AIR and +24V_PROXY outputs are activated. The +24V_AIR is used for solenoid controlling a spring
returned air cylinder, which lowers the proximity switches to the height of tip of the torch. When the torch is
lowered to the cutting height, the proximity switch is activated (the NPN_PROXY input switched to 0V), the
down movement and +24V_AIR output are deactivated, what retract the proxy switches to the safe position
and plasma on relay is activated, this starts the plasma cut. When +PLASMA is off the up movement is
activated. 953-000
[953004.doc 1/13/2002]


� 2001 RUTEX, P O Box 3500, Wamberal 2260, Australia, ph +61-4-1828 3157 (
http://rutex.com
)
2
+
-
DIFFERENTIAL AMPLIFIER
+
-
ERROR AMPLIFIER
THC ENABLE
DOWN
UP
-V
+V
0
SPEED
GAIN
+THC
+DN
+UP
ARC_VOLTAGE1
ARC_VOLTAGE2
REF
+
-
ERROR AMPLIFIER
+
-
BACK EMF INTEGRATOR
0
0
IN OUT1
OUT2
PWM DRIVER
+PLASMA
+AUTO
NPN_PROXY
+UP
+DN
PLASMA_ON
+24_AIR
+24_PROXY
AUTO SEQUENCE LOGICS
+PLASMA
+AUTO
NPN_PROXY
+UP
+DN
PLASMA_ON
+24_AIR
+24_PROXY
+PLASMA
+AUTO
PLASMA_ON
NPN_PROXY
+24_PROXY
+24_AIR
PLASMA_ON1
PLASMA_ON2
MOTOR2
MOTOR1
THC
SERVO DRIVER
Fig. 1.

Interfacing:
Fig 2. and 3. shows the typical connection of 953-002 control system. Both examples use same interface to
the plasma unit, CNC controller and cutting torch. The differences are only in the connection of mode
selection switches. The whole control system must be supplied from DC 24V power supply; capable
delivering enough current for all outputs (motor, solenoid, etc.) plus few hundreds of milli-amperes for 953-
000 PCB. Usually, the 4 amperes power supply is enough.
LM336-5
PLASMA_ON
TCH_ON
10K
3K3
AUTO_INIT
UP/DOWN
ARC_VOLTAGE
MULTITURN POT WITH DIAL
MOT1
1
MOT2
2
+24V
3
+PROXY
5
+24_AIR
6
+PLASMA
8
PLASMA_ON1
9
PLASMA_ON2
10
0V
4
NPN_PRXY
7
THC_EN
11
ARC_VOLTAGE1
12
ARC_VOLTAGE2
14
0V
13
+UP
1
+DN
2
+THC
3
REF
4
+AUTO
5
+AUTO
6
+PLASMA
7
+PLASMA
8
THC_EN
9
THC_EN
10
0V
11
0V
12
+24V
13
+24V
14
CONNECTED TO INTERNAL CIRCUIT
RELAY OUTPUT 5A CONTACT
J2
J1
953-000
ARC_VOLTAGE2
SCREEN
ARC_VOLTAGE1
PLASMA_ON2
PLASMA_ON1
ARC_ON_RLY2
ARC_ON_RLY1
THC_EN1
THC_EN2
ARC_ON-SENCE2
ARC_ON-SENCE1
PLASMA_START2
PLASMA_START1
+24
+24
0V
CNC CONTROL
PLASMA UNIT
A
-
+
UP/DOWN DC MOTOR
LIMIT_1
LIMIT_2
100V/3A
100V/3A
+Vin
GND
OUT
PROXY_NPN
+Vin
GND
OUT
PROXY_NPN
AIR_VALVE
CUTTING TORCH ASSEMBLY
+24
0V
24V/~3A
+24
0V
0V
+24
Fig. 2.
953-000
[953004.doc 1/13/2002]


� 2001 RUTEX, P O Box 3500, Wamberal 2260, Australia, ph +61-4-1828 3157 (
http://rutex.com
)
3
MOT1
1
MOT2
2
+24V
3
+PROXY
5
+24_AIR
6
+PLASMA
8
PLASMA_ON1
9
PLASMA_ON2
10
0V
4
NPN_PRXY
7
THC_EN
11
ARC_VOLTAGE1
12
ARC_VOLTAGE2
14
0V
13
+UP
1
+DN
2
+THC
3
REF
4
+AUTO
5
+AUTO
6
+PLASMA
7
+PLASMA
8
THC_EN
9
THC_EN
10
0V
11
0V
12
+24V
13
+24V
14
CONNECTED TO INTERNAL CIRCUIT
RELAY OUTPUT 5A CONTACT
J2
J1
953-000
2K - 10K
UP/DOWN
ARC_VOLTAGE
MULTITURN POT WITH DIAL
ARC_VOLTAGE2
SCREEN
ARC_VOLTAGE1
PLASMA_ON2
PLASMA_ON1
ARC_ON_RLY2
ARC_ON_RLY1
THC_EN1
THC_EN2
ARC_ON-SENCE2
ARC_ON-SENCE1
PLASMA_START2
PLASMA_START1
+24
+24
0V
CNC CONTROL
PLASMA UNIT
A
-
+
UP/DOWN DC MOTOR
LIMIT_1
LIMIT_2
100V/3A
100V/3A
+Vin
GND
OUT
PROXY_NPN
+Vin
GND
OUT
PROXY_NPN
AIR_VALVE
CUTTING TORCH ASSEMBLY
+24
0V
24V/~3A
+24
0V
0V
+24
+UP
1
+DN
2
+THC
3
REF
4
+AUTO
5
+AUTO
6
+PLASMA
7
+PLASMA
8
THC_EN
9
THC_EN
10
0V
11
0V
12
+24V
13
+24V
14
J3
START
STOP
THC
AUTO
POT_HI
1
POT_ADJ
2
POT_LOW
3
+DN
1
+24
2
+UP
3
J4
J5
952-000
IDC RIBBON CABLE
Fig. 3.

CNC controller:
A dry relay contact should be activated between PLASMA_START1 and PLASMA_START2 to start the
plasma unit. A 24 V output from CNC controller connected to PLASMA_START2 can be used instead of
relay output. The controller to signalize to the CNC that manual start of the plasma has been activated can
also sense this line. A DC 24 V can be sensed between ARC_ON-SENSE1 and ARC_ON-SENSE2. This is
usually used to start the motion of machine. If the CNC controller requires a dry contact or different level of
signal, insert a coil of additional 24V relay between ARC_ON-SENSE1 and ARC_ON-SENSE2 and with
contact of the relay simulate the level, which is required. The CNC controller should provide a normally
closed contact, which disables the THC while the machine, does not cut at full cutting speed (e.g.. when is
slowing down on the sharp corners or during lead-in or lead-out). This contact should be connected between
THC_EN1 and THC_EN2.
PLASMA UNIT:
The plasma unit must be able to be started from external contact. This contact is between PLASMA_ON1
and PLASMA_ON2. As well the plasma unit must have an output, which signalize that the arc is on. This is
usually done by a current relay inside the plasma unit, which close the contact between ARC_ON_RLY1 and
ARC_ON_RLY2. If this signal is not a dry contact or DC +24V, connect a coil of additional relay to this signal
(coil rated same as value of this signal e.g.. AC 110V) and use contact of this relay to close ARC_ON_RLY1
and ARC_ON_RLY2 lines. Many of plasma units have already build in a voltage divider of the arc voltage.
This is usually 25:1, 50:1 or 100:1. The voltage from this divider should be applied to ARC_VOLTAGE1
andARC_VOLTAGE2. A twisted pare screened cable should be used and screen should be terminated only
on one end. If the plasma unit does not have suitable voltage divider installed, please see section Selection
of voltage divider for arc voltage. This divider should be fitted inside, or very close to, the plasma unit to
decrease the possibility of radiation of noise from arc current. 953-000
[953004.doc 1/13/2002]


� 2001 RUTEX, P O Box 3500, Wamberal 2260, Australia, ph +61-4-1828 3157 (
http://rutex.com
)
4
CUTTING TORCH MOVEMENT ASSEMBLY:
The up and down movement of the torch must be motorized and driven by standard permanent magnet DC
24V motor. The limit switches for upper and lower limit should be normally closed and the contact should be
bridged with diode that allows driving only to the opposite direction of the position of the limit. If initial height
sensing is used, one or more normally open NPN type proximity switches should be used together with
solenoid valve for air, which activates the spring, returned air cylinder for lowering the proxy switches to the
height of the tip. The proximity switches can be substituted with mechanical switches with extended
actuators and air cylinder together with solenoid valve can be substituted with electromechanical solenoid.
The electromechanical solenoid should lower the actuators of the switches below the tip of torch, and when
the actuator tough the plate solenoid should retract the switches above the tip of torch.

Mode selection switches:
In the second example (Fig.3.), connection to switches is simplified by using the 952-000 PCB. This PCB is
also available from Rutex. See appendix B for description of this PCB. When installing this PCB, four
switches (PLASMA START, PLASMA STOP, AUTO and THC) are fitted on the front panel and 952-000 PCB
is directly soldered onto these switches. The up/down switch and the potentiometer for arc voltage are
connected via screw-in terminals. The 952-000 and 953-000 PCB are connected with 16 ways ribbon cable.
The first example (Fig. 2.) is hardwired version of 953-000 PCB.

Test circuit:
The Fig. 4. shows a bench test circuit of 953-000 board. This setup should be used before the first
installation or when testing a different type of motor etc.
MOT1
1
MOT2
2
+24V
3
+PROXY
5
+24_AIR
6
+PLASMA
8
PLASMA_ON1
9
PLASMA_ON2
10
0V
4
NPN_PRXY
7
THC_EN
11
ARC_VOLTAGE1
12
ARC_VOLTAGE2
14
0V
13
+UP
1
+DN
2
+THC
3
REF
4
+AUTO
5
+AUTO
6
+PLASMA
7
+PLASMA
8
THC_EN
9
THC_EN
10
0V
11
0V
12
+24V
13
+24V
14
CONNECTED TO INTERNAL CIRCUIT
RELAY OUTPUT 5A CONTACT
J2
J1
953-000
A
-
+
UP/DOWN DC MOTOR
PROXY_SW
AIR_ON
PROXY_ON
PLASMA
AUTO
THC
UP/DOWN
PLASMA_ON
+24
+24
+24
0
10K
10K
5V1/0.4W
2K2
0
+24
Fig. 4.
9