Teledyne BDS-3960 operating instructions Gas Factor, Parameter Selection Box

Maintenance BDS 3960

Select Factor to Adjust

Filter Gas Factor Tmp. Coeff.

Figure 4.2: Parameter Selection Box

4.3.2.1THE DIGITAL FILTER

The Analyzer software performs a digital operation to reduce the noise from the BDS sensor and amplifier. This filtering is reduced to around 10 ppb. If the signal exceeds 10 ppb, the filter disengages in order to track the transient faster. The number approximately corresponds to the response time of the filter in minutes from 10 to 90

%.The range is from 1 to 60 minutes of the 90 % response time. Five minutes is the default.

4.3.2.2 The Gas Factor

The gas factor coefficient in the BDS 3960 is the ratio of the output of the sensor taken in a N2 background over the output of the sensor in the new background gas. The output of the sensor depends on the mechanics of diffusion. Since the diffusion coefficient of oxygen depends on the viscosity of the background gas, according to the laws of diffusion, the output of the sensor becomes inversely proportional to the viscosity of the background gas.

The output of the sensor can be predicted by looking up the viscosity of the new background gas and compare it to the viscosity of N2 at the same temperature. Using values obtained from the a science handbook, the following gas factor coefficients for the BDS sensors are calculated

Table 4-1: Gas Factor for Selected Gases

N2 = 1*

H2= 1.99

He= 0.90

Ar= 0.79

Teledyne Analytical Instruments 46