Startup and operation
RES-430
25
9.5.4
Temperature sensor
The maximum permissible temperature of the sensor
can be set with step 246 (assuming the temperature
sensor has been activated with step 241). An alarm is
immediately output by the controller if this maximum
temperature is exceeded.
If a heatsealing cycle is in progress, it is interrupted.
The temperature monitoring function is activated 3s
after the controller is switched on.
If a temperature sensor is not connected (or if the
sensor connecting cable is defective), an alarm is
output by the controller after 3s (assuming the tempe-
rature sensor has been activated with step 241).
The sensor temperature measurement
described here serves to monitor and/or limit
the load cell or machine temperature. It cannot be
used to monitor the temperature of the heatsealing
band or for temperature control.
9.6
Heatsealing band
9.6.1
General
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 elec-
trical properties:
The measuring principle applied for this system neces-
sitates a heatsealing band alloy with a suitable tempe-
rature coefficient TCR, i.e. one whose resistance
increases as the temperature rises.
Too low a TCR leads to oscillation or uncontrolled hea-
ting.
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 appro-
ximately 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 appro-
ximately 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 (
the heatsealing band" on page 25).
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 heatse-
aling band.
An overheated or burned-out heatsealing
band must no longer be used because the
TCR has been altered irreversibly.
9.6.2
Burning in the heatsealing band
If a new heatsealing band has been used, the zero
point is first of all calibrated while the band is still cold
by activating the "AUTOCAL" function on the controller.
When the "AUTOCAL" function has finished, the dis-
play shows the preselected calibration temperature
(default value: 20°C). Adjust the set point to approxi-
mately 250°C and press the "HAND" key (display in
home position) to activate the "START" signal and heat
for approximately 1 second. After recooling, the con-
troller usually indicates a value less than 20°C. Repeat
the "AUTOCAL" function. The heatsealing band has
now been burned in and the change in the alloying pro-
perties stabilized.
The burn-in effect described here does not occur if the
heatsealing band has already been thermally pre-
treated by the manufacturer.
RES-430
26
Temp.
sensor
0V
27
ϑ
Maximum
Temperature
Time
Error message
sensor temp.
0
!
!
