Sierra 840, 860, 830 instruction manual 880

Appendix A Series 830/840/860 Instruction Manual

Where:

H = The constant amount of heat applied to the sensor tube,

m• = The mass flow rate of the gas (gm/min)

Cρ = The coefficient of specific heat of the gas (Cal/gm);

Cρ is given in the Table (at 0°C),

∆T = The temperature difference between the downstream and upstream coils, and

N= A correction factor for the molecular structure of the gas given by the following table:

Number of Atoms in the Gas Molecule	N
Monatomic	1.040
Diatomic	1.000
Triatomic	0.941
Polyatomic	0.880

The mass flow rate, m,• can also be written as:

•	(3)
m = !Q

Where:

ρ= The gas mass density at standard conditions (g/l); ρ is given in the tables (at 0°C, 760 mm Hg).

Furthermore, the temperature difference, ∆T, is proportional to the output voltage, E, of the mass flow meter, or

∆T = aE (4)

where:

a = A constant.

If we combine equations (3) and (4), insert them into equation (2), and solve for Q, we get

Q = (bN/ρCp) (5)

where:

b = H/aE = a constant if the output voltage is constant.

A-4 IM-83/84/86-H