MNA0010, Revision B October 2014
11
1.3.5
Control Panel:
The Control Panel serves as the main user interface. The Control Panel
features the
keypad
(ramp-up, ramp-down, and mode keys) and the
status LEDs
The control panel is
designed to be splash and water resistant. At the four corners of the panel are the #8-32 mounting studs
which allow flush mounting of the instrument to a control or equipment panel.
1.3.6
Sensor:
The Neutronics Inc.
ZR-400 mini Zirconia
sensor for
measuring PPM range oxygen is a cost
effective solution for many applications.
It is a solid state device based on a
Zirconia solid electrolyte sensor with a
low power, on -board heater. Unlike
many solid state oxygen sensors, the
ZR-400 does not require a reference
gas for normal operation. The sensor
operates in a current limiting type
configuration. The basic electrical
diagram of the sensor is in figure 5:
The sensor is an electrochemical cell which measures oxygen. The sensor itself is mounted directly
onto a printed circuit board (see figure 6). The circuit board controls sensor excitation voltage and
also the heater voltage. Basically, a voltage is applied to the sensor element. Diffusion of oxygen into
the sensor is controlled by a small capillary on the sensor surface. At operational temperature,
oxygen is electrochemically reduced at the cathode. Oxygen concentration in the sample gas is
determined by measuring the current flowing through the S+ and S- terminals of the sensor. The
robust design of the sensor assures accurate measurement as well as a quick response characteristic
to serve a wide range of oxygen measurement applications. A major advantage of the ZR-400
sensor is that it is not affected by the position.
Additionally, there exists no real limitation on shelf life or storage temperature. Sensors may be
exposed to severe temperatures and perform to specification once brought up to operating conditions.
The sensor may be exposed to several G-Force with no ill effect on performance. Perhaps the most
attractive feature of the ZR-400 is its long life. Expected operating life is five years under normal
operating conditions!
Figure 6: Installation of the Mini-Zirconia oxygen sensor on the controller board / Cell Block.
H
H
S +
S-
A
Ammeter
Sensor Power: 0.8 Vdc
+ 0.01V
Heater Power: 4.5 Vdc
+ 0.1V
Mini-ZrO2
Sensor Circuit
Figure 5