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After the electronics have been properly zeroed (a one-time factory operation), the instrument
cannot produce an output indication in the absence of oxygen; therefore, the need for a “zero”
standardization gas is obviated.
1.3.3 Integral Power Supply
: The differential power and digital panel meter
(DPM) requirements of the instrument amplifier are furnished by three internally-mounted 750
milliampere-hour nickel-cadmium batteries. Fully charged, these batteries will provide enough
power to operate the instrument continuously
for a period of ca. 500 hours. Furthermore, an
overnight charge on a 2-day duty cycle should keep the original batteries usable for many years.
A “LOW BATTERY” indication is shown on the digital display.
An integral charging circuit and a detachable power cord are provided so that the batteries may
be recharged from any 50 or 60 cycle, 105 to 125 volt convenience outlets.
The instrument is designed to either sample or have its batteries recharged. Both operations
cannot be carried out simultaneously. TAI has deliberately interlocked the circuitry in this way.
Only when the selector switch is placed in the “OFF” position will the neon lamp on the back
plate of the 311D light up to indicate power to the battery charging circuit.
A current limiting resistor (53.2 ohms) is potted into the end of each battery. This assures that,
under no circumstances, can more than 80 milliamperes be switched or drawn from either battery
supply.
BATTERY CHECK
: To determine the state of the rechargeable batteries, turn the range
selector knob counter-clockwise to the battery test position and hold there; the switch is spring-
loaded, and must be held. The meter should read more than 1600; otherwise, the batteries need
to be recharged. Release the Range Selector Switch, and it will automatically return to the
“OFF” position. When the batteries are set at a really low charge condition, the “LOW BATT”
warning is displayed. Caution should be taken not to discharge the batteries any further.
1.3.4 Accuracy and Response
: The Model 311D provides monitoring accuracy
of ±0.2% of full scale, or ±0.2 ppm, whichever is greater, at constant temperature. A ±5% of
reading accuracy is achievable throughout the operating temperature range of 30 to 125°F.
With a sample flowrate of 150 cc/min., 90% response is achieved in 10 seconds in all the
positions.
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1.3.5 Compact Packaging
: The instrument is housed in a 6-1/8 x 9-1/2 x 5-5/8
inch aluminum case that is equipped with a carrying handle and foot pads.
Access to the instrument interior is gained by loosening (ccw) the three 1/4” slot-head fasteners
on the back of the outer case. The case may then be detached from the control panel assembly.