Section 3 - Theory of Operation
A 4-20 mA loop is a series loop in which a transmitter will vary the current flow
depending on the input to the transmitter. In the EWS-BP-A the amount of current allowed
to flow in the loop will vary depending on the atmospheric pressure being measured by
the sensor. Some advantages of a current output over a voltage output is that the signal
measured is less susceptible to electrical noise interference and the loop can support more
than one measuring instrument as long as the maximum loop resistance is not exceeded.
A typical application utilizing a current loop will normally consist of a power supply, the
transmitter and a meter, recorder or controller to measure the current flow. The loop
resistance in the sum of the measuring instruments and wire used. The maximum
allowable loop resistance for the EWS-BP-A to function properly is found by using the
following formula:
Rmax = (power supply voltage – 8 volts) / .02 amps
For applications that require a voltage output signal the EWS-BP-A has a built-in 250 Ohm
shunt resistor that will convert the transmitters output to a 1-5 Vdc signal when wired
correctly. See "Transmitter Wiring Examples" in this manual.
Section 4 - Specifications
Range:
20.8 to 32 in Hg (10.20 to 15.72 psi)
Accuracy:
±1% FSO
Repeatability:
±.2% FSO
Pressure Hysteresis:
±.15% FSO
Long–Term Stability:
±.1% FSO/Year
Operating Temperature Range:
-20 to 140ºF (-29 to 60ºC)
Temp. Compensation Range:
32 to 140ºF (0 to 60ºC)
Output:
4 – 20 mA or 1 –5 Vdc (scaled to full range)
Power Requirements:
For 4-20 mA output:
12 –24 Vdc @ 20mA
For 1-5 Vdc output:
13 –24 Vdc @ 20mA
Max Loop Resistance:
Ohms = (V supply – 8 V) / .02 A
RH Time Constant:
1 ms., from 10-90% FSO
Sensor Type:
Solid State
Media Compatibility:
Clean room air with a relative humidity less than 90%
(non-condensing), non-corrosive gases
Enclosure Material:
Acrylonitrile Butadiene
Dimensions:
79 x 54 x 45mm (3.12 L x 2.12 W x 1.78" H)
Weight:
54 g. (.12 lbs)
These units are not designed, nor recommended for medical use,
explosive environments or outdoor applications.
2
NOTE:
