RLE 10K V.2.5.a - Manual (Page 35)

rletech.com SeaHawk 10K User Guide 35
4 Modbus Communication
4.4. Calibrate Cable Length via Modbus
The length of sensing cable connected to the SeaHawk 10K can be calibrated through a
Modbus-enabled system. This helps fine-tune a distance-read leak detection system. If no
alarms are present, follow these steps to calibrate and test the system:
1 Set the SW1 DIP switches for the correct cable resistance per foot, as follows:
Figure 4.1 DIP Switch Settings for Ohms/Foot
2 Press the Test/Reset button on the controller once to verify the cable’s amperage reading.
Calibration cannot be performed if the current is above 15 μA.
Different sensing cables are cleaned in different ways. The following cleaning instructions
apply to RLE’s orange sensing cable ONLY! If you have questions regarding the care and
maintenance of your sensing cable, please consult the cable’s data sheet or contact the
manufacturer.
If the cable is new and the current is higher than 1 μA, clean the cable. Isopropyl alcohol
removes any contamination that might have been introduced to the cable during installation.
If the cable is older and the amperage reading is above 15 μA, clean the cable. A mild dish
detergent solution removes most dirt. Isopropyl alcohol is also an effective cable cleaner.
3 Sensing cable has a resistance - for example, RLE’s orange cable has a resistance of 2.8
ohms per foot. A system's actual resistance will rarely be exactly 2.8 ohms per foot, but it
will be close - each individual cable or system will vary a very small bit from that 2.8 ohms
per foot value. If you know the exact resistance of your cable, you can fine-tune your
system for a more precise distance reading. The formula for calculating this value - and
more specific directions for using the formula - are as follows:
Figure 4.2 Formula for Calculating Exact Cable Resistance
4 Read the Leg 1 and Leg 2 Resistance values in Modbus registers 30006 and 30007. Ensure
that the reading are similar - within 2% of each other. This helps rule out any major cable
problems before calibration begins. Record the resistance reading from Leg 2, Modbus
register 30007.
Leg2 Resistance (Modbus register 30007)
(Modbus register 40008)
Resistance per foot
in milliohms/foot
Total Feet of Cable Installed on the System
X
1000