Teledyne 300P - Percent oxygen analyzer - Manual (Page 9)

2-3 Teledyne Analytical Instruments
Percent Oxygen Transmitter Operational Theory 2
with lower temperature, down with higher temperature) so that the output
of this stage is constant over the temperature range at any given O
2
concen-
tration.
The output voltage-to-current stage (E to I) draws 4 mA from the
power supply loop when there is no oxygen present in the sample gas, and
20 mA when there is full scale oxygen present in the sample gas. It also
supplies the +5V and -5V required by the circuitry.
A 24V power supply is recommended to power the transmitter for
most applications. The actual minimum and maximum values of this
supply depend upon the total loop resistance, which consists of the input
resistance of the receiver and the resistance of the wires between the trans-
mitter and the power supply. Power applied across the terminals of the
transmitter must be between 14V and 30V. Using this criteria, the maxi-
mum line resistance can be determined. For example, with a 24V power
supply, a maximum of 10V is available (24V-14V) for drop across the
input resistance of the receiver and the line resistance. This amounts to a
maximum loop resistance of approximately 500 ohms (10V divided by
0.02A).
The B-2 or B-2C cell used in this instrument normally generates
about 500
µ
A output current in air (20.9% O
2
). This is about 2 nA per
ppm.
2.4 RFI Protection
The Model 300P is designed to be RFI protected by virtue of the
electronics being mounted inside a grounded metallic enclosure. The RFI
protection, therefore, is maximized when the enclosure door is closed.