Startup and operation
Page 16
RES-402
Version 1
If the secondary current I
2
is less than 30A, the secondary high-current wire must be laid twice (or several times)
through the PEX-W3 or PEX-W4 current transformer (
ROPEX Application Report).
6.3
Replacing and "burning in" the heatsealing band
6.3.1
"Burning in" the heatsealing band
The heatsealing band is a key component in the control loop, since it is both a heating element and a sensor. The
geometry of the heatsealing band is too complex to be discussed at length here. We shall therefore only refer to
a few of the most important physical and electrical properties:
The measuring principle applied for this system necessitates a heatsealing band alloy with a suitable temperature
coefficient TCR. Too low a TCR leads to oscillation or uncontrolled heating.
When heatsealing bands with a higher TCR are used, the controller must be calibrated for this.
The first time the heatsealing band is heated to approximately 200…250°C, the standard alloy undergoes a once-
only resistance change (burn-in effect). The cold resistance of the heatsealing band is reduced by approximately
2…3%. However, this at first glance slight resistance change results in a zero point error of 20…30°C. The zero
point must therefore be corrected after a few heating cycles, i.e. the AUTOCAL function must be repeated.
The burn-in effect described here does not occur if the heatsealing band has already been thermally pretreated
by the manufacturer.
An overheated or burned-out heatsealing band must no longer be used because the TCR has been
altered irreversibly.
One very important design feature is the copper or silver-plating of the heatsealing band ends. Cold ends allow
the temperature to be controlled accurately and increase the life of the teflon coating and the heatsealing band.
6.3.2
Replacing the heatsealing band
All power supply leads must be disconnected from the RESISTRON
®
temperature controller in order
to replace the heatsealing band.
3
2
1
4 5
ON
OFF
1...10V
6...60V
20...80V
ON
OFF
OFF
OFF
ON
OFF
OFF
OFF
ON
30...100A
60...200A
120...400A
OFF
ON
ON
OFF
OFF
ON
DIP switch
DIP switch
1 2
U
2
I
2
3
4
5
3
2
1
4
5
4
3
O
N
O
F
F
U
(
V
)
2
1-
10
SW
IT
C
H
ON
Factory settings
2x
!
!
