APPLICATION CONSIDERATIONS
7
3. Automatic calibration on single thickness steel after coil change (Switch 6 ON). In this
mode, calibration process is the same as for the manual single-hit calibration except that the
calibration process can be initiated by the expiration of a timer within the DS1522. The
timer can be set to a value from 0.1 minute (6 seconds) to 25 minutes. When the DS1522
detects the absence of material between the probes, the timer count-down begins. If the
count-down expires before material is sensed, the DS1522 enters calibration mode, waiting
for material to be fed. If the calibration delay parameter (Cd) is set to zero, calibration
occurs within 100 milliseconds after material is sensed between the probes. For slow moving
material, this delay can be increased (up to 9.9 seconds) to insure the material fully covers
the probes before calibration occurs. See the Control Module Calibrate Pushbutton
section earlier in this document for the parameter adjustment procedure.
4. Automatic calibration on single thickness steel after double (overlap) detected (Switch 1
ON). In this mode, available in systems with Firmware Version 2.1 and higher, the
calibration process is the same as for modes 2 and 3 above except that the calibration process
is initiated by the occurrence of a lap weld or overlap in the incoming material. When the
OVER condition is detected, the OVER relay switches for a minimum of 25 milliseconds and
then after the programmed calibration delay (Cd) calibration commences. The intent of this
mode is to detect lap joints and provide automatic recalibration on the material following the
lap joint.
When automatic calibration after double is enabled (Switch 1 ON), the calibration delay (Cd)
parameter may be used to insure calibration occurs beyond the overlap area. However,
should calibration occur on the overlap, the detection of an under condition after the overlap
will initiate recalibration if the under tolerance is set appropriately. The delay of relay
response through the “ry” parameter may still be used in this mode. However for detection
of short overlaps it may be necessary to set the relay delay to zero for fastest gauge response.
The choice of calibration mode is application dependent since each mode has its advantages and
disadvantages. Two-hit calibration offers the possibility of discriminating changes in metal
thickness that are far less than 2 to 1 since the system is calibrated on samples of the thickness
range to be discriminated.
Relay Response Time
For most applications it is desirable that the OVER relay respond as quickly as possible. For
thinner materials the response time is as fast as 3 milliseconds. For very thick metals the
response time can be as long as 40 milliseconds.
If very fast response times are undesirable, the action of the relays can be delayed through the
adjustment of the relay delay parameter (ry). This parameter represents a time interval in
fractions of a second from .00 to .99 seconds. To adjust the delay value, press and hold the CAL
pushbutton until the identifier “ry” appears on the two digit display. Release the pushbutton and
observe the current value of the delay parameter. Press and/or tap the CAL pushbutton as
necessary to bring the delay parameter to the desired value. To retain the adjusted value of the
parameter, simply allow the 5 second display interval to elapse. The display reverts back to
