Basic Controls—System 350 P352AB Electronic Pressure Control Series Product/Technical Bulletin
9
c. The transducer output signal voltage (
Vo
)
increases proportionally to an increase in the
pressure at the transducer (
psi
T
). Use the
graph in Figure 8 to compare the measured
signal voltage to the measured pressure or
use the formula below to compare the voltage
and pressure values.
psi =
T
10
V
o -
o
(
)
VDC
S
x
P
max
1.25 x
VDC
S
psi
T
= Pressure measured at transducer
Vo
= Transducer output signal voltage (VDC)
VDC
S
=Supply voltage to the transducer
(measured in step 2a).
P
max
= Transducer pressure range maximum
Example:
The measured pressure at the gauge is
approximately 245 psi (
psi
T
), the measured
transducer output voltage is 2.5 VDC (
Vo
), the
measured supply voltage to the transducer is
5.03 VDC (
VDC
S
), and the transducer’s rated
range is 0 to 500 psi (
P
max
). Use the formula
above to calculate the pressure you would
expect from the measured voltage.
2.5 -
(
10
5.03 x
)
1.25 x 500
5.03
= 248.1 psi
Since the measured pressure of 245 psi (
psi
T
)
is close to the pressure calculated from the
measured voltage of 248.1 psi, the transducer
output voltage is considered within the desired
range.
Note:
Depending on the accuracy of the
instrumentation used to measure the
actual pressure at the transducer
(
psi
T
) and the transducer output
voltage (
Vo
), the actual and calculated
pressure may not exactly agree.
(10%)
(90%)
(50%)
Output Voltage
(% of Power Supply)
4.5 VDC
2.5 VDC
0.5 VDC
500 psi
P352AB-3
P399B
Pressure (psi)
P352AB Model
P399 Transducer
100 psi
P352AB-2
P399A
P
35
2A
B
-2
P3
52
AB
-3
P3
52
AB
-4
Figure 8: Pressure vs. Output Voltage
4. Check the control for proper operation.
Perform Steps 1-3 first.
Note: When the LED is lit, the N.O. contacts are
closed.
a. Determine and record if the control is
in the DA or RA mode of operation.
b. Determine the differential setting.
c. Observe and record the system
pressure at the gauge.
d.
If the control is in the DA mode
, adjust the
setpoint setting to a value lower than the
observed gauge pressure. If the LED is not lit,
turn the setpoint adjustment knob
counterclockwise until the LED lights
e. With the LED lit, slowly turn the setpoint
adjustment knob clockwise (to increase the
setpoint setting) until the LED goes off.
Observe the gauge pressure, which should be
the same as the setpoint setting when the LED
goes off.
f.
Next turn the setpoint adjustment slowly
counterclockwise until the LED lights again.
Observe the gauge pressure, which should be
equal to the differential setting plus the
setpoint setting when the LED lit.