Sierra Monitor Corporation 4105 manual Calibration

5.CALIBRATION

5.1 Frequency of Calibration

The manufacturer recommends that the gas sensor module be calibrated every ninety days.

5.2 Calibration Process

The output signal of the gas sensor module is cali- brated using a span mixture containing a known con- centration of the gas of interest. The concentration of the span gas must be within the full scale of the sensor module and should be either 50% of the full scale, or approximately equal to the lowest alarm level.

Calibration requires application of the span gas to the sensor and adjustment of the “SPAN” magnetic switch making the module signal output and display equiva- lent to the concentration of sample gas. The 4-20 mA output is held at 1.5 mA while activated for calibration to prevent alarms being tripped by calibration gas application.

5.3 Equipment Required

The following tools and equipment will be required for calibration:

-Magnetic tool

-Gas Sensor Calibrator, Model 1260-XX or Model 1200-26 or permeation tube

-Calibration Gas

-Disbursing Calibration Adapter (Model 5358- 01)

5.4Calibration Procedure

Routine calibrations are easily performed using the magnetic tool provided with each sensor.

Briefly hold the magnet tool close to the small dot located on the lower edge of the front panel. The arrow on the upper left side of the LED will illuminate and the 4-20 mA output is locked at 1.5 mA, indicating that the sensor module is ready for calibration. Sim- ply expose the sensor to a ZERO gas and observe the L.C.D. readout. In normal situations, simply exposing the sensor to an atmosphere free of the gas of interest is satisfactory. If it does not return to the correct ZERO reading, a ZERO adjustment is required. Hold the magnet close to the UP ZERO or DOWN ZERO indicators and adjust the reading to the correct ZERO reading.

Instruction Manual

Connect the calibration adapter and expose the sen- sor to an appropriate SPAN gas using a span mixture containing a known concentration of the gas of inter- est at a minimum flow rate of 300 cc/minute. (Use per- meation tube for 4105-25) Allow 3-5 minutes before making any adjustments.

If the L.C.D. does not display the correct SPAN value, a SPAN adjustment is required. With the arrow still flashing, hold the magnet close to the UP SPAN or DOWN-SPAN indicators and adjust the reading to the correct SPAN value. (The 4-20 mA out is automati- cally adjusted.)

The monitor is now calibrated. Deactivate calibration by holding the magnet close to the small dot again. This releases the 1.5 mA lock.

5.5 Fault Identification

A Fault condition is detected if the sensor output drifts far enough negative to cause the 4-20 mA output to reach 1.5 mA (±15% of full scale) or the sensor failure. The sensor module demonstrates that a fault condi- tion exists by illuminating the RED LED on the front panel and by holding the 4-20 mA output at 0 mA. These conditions will exist until the fault is corrected.

Model	Gas	Min. Flow Rate
		(cc/min)
4105-02	CH4	100
4105-03	O2	100
4105-04	CO	150
4105-05	H2S	300
4105-06	Cl2	300
4105-07	H2	300
4105-10	SO2	300
4105-12	NO2	300
4105-21	HCl	300
4105-22	HCN*	300
4105-25**	NH3	400
4105-26	HF	500

*Note: SO2 may be used instead of HCN to

calibrate: 10ppm SO2 = 16 ppm HCN

*Note: H2S may be used instead of HCl to

calibrate: 10 ppm H2S = 20 ppm HCl

** Note: Use permeation tube for 4105-25

Table 4.1

Calibration Span Gas Flow Rates

Model 4105 Gas Sensor Module (12/02) Page: 5