Download FEATURES: INTRODUCTION: GENERAL CIRCUIT DESCRIPTION

CDI Universal Evaluation Board
Designed For Use With The GE/NovaSensor
Pressure Sensors Series NPC-1210 and NPH-8
FEATURES:
• Instant Prototyping
• Selectable Voltage Outputs
• Pressure Ranges From 10”H20 to 100 psig or psia
• Compatible with the NPC-1210 and NPH-8 Sensors
INTRODUCTION:
The CDI Universal Evaluation Board has been designed for use with the GE/NovaSensor pressure sensors series NPC-1210 and the NPH-8. The board is intended to expedite the bread boarding of almost all
pressure sensor applications. While the board will come pre-calibrated for an output of 0.5 V to 4.5 V for
any pressure range between 10” water to 100 psi, the user can easily change the output by recalculating
the gain, and changing a couple of resistors. Below you will find a general description and examples.
GENERAL CIRCUIT DESCRIPTION:
To explain how the CDI Universal Evaluation Board works, the circuit is shown in Figure 1, and is
broken down into three sections.
Vss SENSOR SELECTION:
Connecting the solder shorts
The first step in using the CDI Universal Evaluation Board is to make
sure that the correct solder shorts
are connected. Referring to schematic diagram, shown in Figure 1,
as the sensor to be used is a NPC1210 device, solder shorts S1, S2,
S3 and S4 should be shorted via
Solder blobs. (Solder Shorts S5,
S6, S7 and S8 are only used if an
NPH-8 pressure sensor is used.
Vss
R1 10K ohm LT1004‐1.2 Vss 2 V1 3 U1 2 8 LT1490 4 Section 3
7 1 1 S1
U2 R5
4
Rset
R3
1
NPC S3
3
U3 LT1789
Vo= 0.5 to 4.5 V
6 G = 26 to 160 Span Adj 8 3 5 4 S2
2
R2 820 ohms LT1490 R4
5 5
S5
V1
6 7 S4
R6
10
S7
Section 1 NPH
4
S6
Section 2
6
S8 Figure I
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Offset Adj
10K ohm
2.5K ohm
CDI Universal Evaluation Board
Designed For Use With The GE/NovaSensor
Pressure Sensors Series NPC-1210 and NPH-8
Vss SECTION 1: THE CURRENT SOURCE
Vss
R1 This portion of the circuit sets current to
the pressure sensor. The NPC and NPH-8
series sensors should be driven by a 1.5mA
constant current source to achieve the
specified output voltages as shown on the
datasheet, the Iset current is set by the Linear Technology 1.2V voltage reference and
R2. The exact value of Iset will equal:
10K ohm Section 3
2 V1 LT1004‐1.2 Vss 3 2 U1 7 8 LT1490 4 1 1 S1
R5
4
U2 Rset
R3
1
Vo= 0.5 to 4.5 V
6 G = 26 to 160 8 3
NPC S3
U3 LT1789
Span Adj 5 3 4 S2
2
R2 820 ohms LT1490 Offset Adj
R4
10K ohm
5 5
S5
V1
6 7 S4
2.5K ohm
R6
10
S7
Iset = V1/R2 = 1.2V/820 ohms ≈ 1.5 mA
Section 1 S6
4
NPH
Section 2
6
Figure I
S8 Other values of the Iset are possible by adjusting the R2 resistor value. Please note that the output of the
NPC and NPH-8 devices are ratiometric to the supply current. For instance, the value of R2 is changed
from the datasheet. The specified 1.5 mA such that Iset = 0.75 mA, then the output of the sensor will be ½
of the specified output shown on the datasheet.
SECTION 2:
Vss Section 2 of the circuit is simply a
divider network which sets the offset
to the output. The Universal Evaluation Board will be factory set to 0.5 V.
This offset is not part of the amplifier
circuit and should not be interactive
with the gain adjustment.
Vss
R1 10K ohm Section 3
2 V1 LT1004‐1.2 Vss 3 2 U1 7 8 LT1490 4 1 1 S1
U2 R5
4
Rset
R3
1
NPC S3
3
U3 LT1789
8 3 5 4 S2
2
R2 820 ohms LT1490 R4
5 5
S5
V1
6 7 S4
You can adjust the amount of offset
injected into the circuits within the
voltage divider limits.
R6
10
S7
Section 1 NPH
4
S6
Section 2
6
S8 Figure I
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Vo= 0.5 to 4.5 V
6 G = 26 to 160 Span Adj 1-800-777-7334
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Offset Adj
10K ohm
2.5K ohm
CDI Universal Evaluation Board
Designed For Use With The GE/NovaSensor
Pressure Sensors Series NPC-1210 and NPH-8
SECTION 3:
The heart of the CDI Universal Evaluation board is shown in section 3. The Linear Technology LT1789-10
is a micro-powered, single source instrumentation amplifier. The gain is normally set by a single resistor,
however in this circuit, two resistors are used: A fixed resistor and potentiometer. This manner allows for
some gain adjust due to variation in the pressure sensors output and Iset current source.
For a complete understanding of the LT1789, it’s strongly suggested that the Linear Technology datasheet
for that device be reviewed. The gain
of the LT1789-10 is set by the value of resistor RG, applied across
pins 1 and 8. For the LT1789-10, the gain G will be
Vss G =10 • (1 + 200k/RG)
Therefore the value of Rg can
be calculated from the desired
gain by
Vss
R1 10K ohm LT1004‐1.2 Vss 2 V1 3 2 U1 8 4 1 1 LT1490 S1
U2 Rg = 200k/(0.1 • G – 1)
R5
4
Rset
R3
1
NPC S3
From the NPC and NPH-8
datasheet, the sensor can have
various outputs, so Rg needs
to be able to achieve any of
these values.
Section 3
7 3
U3 LT1789
Vo= 0.5 to 4.5 V
6 G = 26 to 160 Span Adj 8 3 5 4 S2
2
R2 820 ohms LT1490 R4
5 5
S5
V1
6 7 S4
R6
10
S7
Section 1 NPH
4
S6
Section 2
6
S8 Figure I
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Offset Adj
10K ohm
2.5K ohm
CDI Universal Evaluation Board
Designed For Use With The GE/NovaSensor
Pressure Sensors Series NPC-1210 and NPH-8
Below is a chart showing the potential value of Rg:
NPC-1210 Low Pressure
Output
Span
Gain (4/Output)
Rset (Ohms)
Min
0.025
4
160.0
13333
Typical
0.05
4
80.0
28571
Max
0.07
4
57.1
42424
Output
Span
Gain (4/Output)
Rset (Ohms)
Min
0.075
4
53.3
46154
Typical
0.1
4
40.0
66667
Max
0.15
4
26.7
120000
Output
Span
Gain (4/Output)
Rset (Ohms)
Min
0.05
4
80.0
2532
Typical
0.075
4
53.3
3822
Max
0.15
4
26.7
7792
Output
Span
Gain (4/Output)
Rset (Ohms)
Min
0.075
4
53.3
3822
Typical
0.1
4
40.0
5128
Max
0.125
4
32.0
6452
Output
Span
Gain (4/Output)
Rset (Ohms)
Min
0.075
4
53.3
3822
Typical
0.1
4
40.0
5128
Max
0.125
4
32.0
6452
NPC-1210 Medium Pressure
NPH-8-007xH Low Pressure
NPH-8-030xH Low Pressure
NPH-8 Medium Pressure
The resistor value for the two resistors is on the Universal Evaluation Board. They are chosen such that, the fixed
resistor is 80% of the values (most of the gain) and the potentiometer can be used to trim the gain to the exact
requirements.
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CDI Universal Evaluation Board
Designed For Use With The GE/NovaSensor
Pressure Sensors Series NPC-1210 and NPH-8
ORDERING INFORMATION:
When ordering the CDI Universal Evaluation
Board, please use the chart below.
UPEB Sensor Type NPC NPH Pressure Range 010 Inches water column 001 PSI 005 PSI 015 PSI 030 PSI 050 PS1 100 PSI Pressure Reference D G A UPEB ‐ XXX ‐ XXX ‐ X 3 inches
0.25” Component Distributors Inc.
www.cdiweb.com
U1
R1 0.25” U2 P1 2 Inches R4 Offset Adj R2 U3 R3 R5 Span Adj
P2 Vout
Vin
Gnd
PressEval01 – Rev A
Note: If you would like a non-standard pressure range, or the device to be calibrated in different units
please contact CDI directly at 1-800-777-7334 or [email protected] and talk with a FAE
before ordering.
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email: [email protected]