RLE GD100 - Manual (Page 18)

CTS-M17 Installation, Operation and Maintenance Manual
B84450-001-000 RG May 12, 2005 17
2.3.2 RS-485 End-of-Line Wiring and Termination
RS-485 installations require specialized wiring. A number of manufacturers make
cable especially for this wiring standard (EIA-485), (e.g. Belden 9841). This is a
twisted, shielded, balanced pair, 24 awg, 120 ohm. In order to prevent signal
bounce-back and other distortions, it is necessary to provide a balancing resistor
across both ends of the wire. The M-17 supplies this resistor on board, and it is
chosen using a jumper at JP2.
Figure 4 - RS-485 End-of-Line Termination (JP2)
2.4 Gas Calibration
Calibration should not vary significantly over a period of years; however, it is best
to perform a verification calibration after installation, and at one-year intervals
thereafter. All units are factory calibrated.
2.4.1 Equipment Required
• Zero air, (must contain oxygen).
• Appropriate span gas, typically about 50% LEL
• Pressure and Flow Limiting Regulator(s) 0.4to 0.8 lpm (0.8 to 1.6 scfh)
• Tubing and bayonet adapter.
Figure 5 - Calibration Gas Bayonet Adapter
2.4.2 Calibration Procedure
Response of this sensor to gas is quite rapid, and the signal should be adequately
stable for adjustment in less than one minute. It is best to allow one hour warm-up
and stabilization time before calibrating.