Portable, Modular Signal Conditioning Modules

6

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NI SCC-SG Series Strain Gage

Input/Excitation

The National Instruments SCC-SG Series consists of dual-channel strain

gage modules for conditioning quarter, half, and full-bridge strain gages

and a calibration module. Each module is designed for a specific type of

bridge configuration. Each channel of an NI SCC-SG module (except

SCC-SG11) includes an instrumentation amplifier, a 1.6 kHz lowpass

filter, and a potentiometer for bridge-offset nulling. Each SCC-SG0x

module also includes a single 2.5 V excitation source. The SCC-SG24

has a 10 V excitation source for load cells and pressure sensors.

The SCC-SG11 is a dual-channel shunt calibration module for use with

the SCC-SG0x and SCC-SG24 modules. Each channel includes two

terminals for wiring a switched 301 kΩ, 1 percent, 1⁄4 W resistor across

any two points of your bridge. You enable shunt calibration for both

channels of a module by writing a logic high to the digital line controlling

the SCC-SG11. You disable shunt calibration by writing a logic low to the

same digital line.

When you install an SCC-SG module in the SC-2345, the carrier routes

the strain gage signals to two input channels of the multifunction DAQ

device, channels x and x+8, where x is 0 through 7.

Specifications

SCC-SG0x

Input Characteristics

Number of channels............................

2 differential

Input signal range ...............................

±100 mV

Output signal range ............................

±10 V

Gain ....................................................

100

Overvoltage protection .......................

Input impedance .................................

10 MΩ powered on, 10 kΩ

powered off or overload

Gain error ............................................

±0.8% of reading maximum

Offset error..........................................

±5 µV

Bandwidth ...........................................

1.6 kHz (single-pole RC filter)

Excitation voltage ...............................

2.5 V ±0.4%

Excitation Current Drive

SG01, SG02 .........................................

42 mA (with 2 120 Ω gages)

SG03, SG04 .........................................

60 mA (with 2 350 Ω gages)

Excitation drift.....................................

13 mV/°C

Power Requirements

Analog .................................................

143 mW

Digital..................................................

210 mW

SCC-SG11

Number of channels............................

2

Control signal ......................................

1 DIO channel

Resistor for each channel ...................

301 kΩ ±1%, socketed

Resistor temperature coefficient........

±100 ppm/°C

Power Requirements

Digital..................................................

25 µW

SCC-SG24

Input Characteristics

Number of channels............................

2 differential

Input signal range ...............................

±100 mV

Output signal range ............................

±10 V

Gain ....................................................

100

Overvoltage protection .......................

±42 VDC powered on and

powered off

Input impedance .................................

20 MΩ powered on >60 kΩ

powered off or overload

Gain error ............................................

±0.20% of reading max

Offset error..........................................

±50 µV typ, 325 µV max before

Bandwidth ...........................................

1.6 kHz single-pole buffered RC

filter

Excitation voltage ...............................

10 V ±0.05%

Excitation current drive.......................

60 mA, based on two full-bridge

350 Ω strain gages

Excitation drift.....................................

10 ppm/°C

Power Requirements

Analog .................................................

340 mW

Digital..................................................

930 mW

1

By factory default, the nulling resistors are not installed in the SCC-SG24. See the user

manual for information on installing the nulling resistors.

Model

Channel

Description

Part Number

SCC-SG01

2

120 Ω, quarter-bridge strain gages

777459-13

SCC-SG02

2

350 Ω, quarter-bridge strain gages

777459-14

SCC-SG03

2

Half-bridge strain gages

777459-15

SCC-SG04

2

Full-bridge strain gages

777459-16

SCC-SG11

2

Shunt calibration

777459-17

SCC-SG24

2

Full-bridge strain gages, load cells,

pressure sensors, torque sensors

777459-37