Bridge and Strain Conditioning Overview

Precision 28000 Solutions for Measuring Static or Dynamic Strain

Precision Filters, Inc. (PFI) offers a complete line of bridge and strain conditioners to measure static or dynamic strain (including high temperature strain) or any bridge type transducer including pressure sensors, piezo-resistive accelerometers, load cells and more. Choose from our line-up of four and eight channel cards with performance to match your requirements.

PFI’s Balanced Constant Current™ technology is the industry’s best technique to measure dynamic strain, even in harsh environments, and uses only a two-wire connection to the gage. The circuit is insensitive to changes in lead resistance with temperature. Because the circuit is balanced, the differential input amplifier rejects noise pickup in the leads. Below are just a few of our recent innovations.

The 28000 Bridge and Strain Conditioning Suite of Cards.

MEASUREMENTS:
- Piezo-resistive Pressure Sensors (Kulite)
- Static or Dynamic Strain
- High Temperature Strain
- Piezo-resistive Accelerometer for Shock
- Static or Dynamic Full Bridge
- Pressure Sensor
- RTD
- Load Cells
- Low-level AC or DC Voltage

Innovative Performance Technologies

Sensor Health Monitoring

At Precision Filters, we know that even the best signal conditioner is of little value if the sensor or input wiring is faulty. A failed sensor or cable discovered after the test is too late and will result in lost data that can never be recovered. Quick and easy visibility of cable and sensor health allows timely corrective actions to save crucial data. Test hardware and software in our bridge conditioner products automate sensor and cable health checks. Transducer excitation, resistance and even leakage to ground are reported in real time.

Balanced Constant Current

Precision Filters’ proprietary Balanced Constant Current (BCC™) excitation is optimized for making dynamic strain measurements on single active strain gages. Balanced constant current excitation provides an accurate means of measuring dynamic strain with a single active strain gage using only a two-wire connection.

BCC excitation provides a true balanced input for rejection of common- mode signals. Electrostatic pickup is reduced when compared to single-ended constant current excitation or a quarter-bridge configuration with remote completion resistors or unbalanced current sources. The balanced current excitation circuit operates properly even under certain common gage fault conditions such as a direct short of the gage to the test model.

Measuring Resonant Transducers

Some transducers such as piezo-resistive pressure transducers can have very high resonant frequencies that can be excited by transient events and this out-band signal can be larger than the signal of interest.

The 28000 amplifier gain is distributed as “pre-filter” and “post-filter” gain to allow the filter to remove out-band signals such as transducer resonance while still achieving the required full-scale in-band signal level. Using the 28000 “reserve” feature, the user can specify the required protection against out-band noise and the pre- and post-filter gain are automatically distributed to provide this protection. The pre-filter gain is set to achieve the required amplifier headroom for the out-band signals prior to the filter while maximizing dynamic range. After the filter removes the out-band signals, the post-filter gain is set to achieve the desired full-scale output. The 28144 card may be equipped with either a low-pass filter or a high-pass filter cascaded with a low-pass filter to form a band-pass filter. The band-pass configuration and the distributed amplifier gain provide the user ultimate flexibility to eliminate sources of either high frequency or low frequency noise.

Frequency or Time Domain Measurements

The Precision Filters’ FLAT/PULSE filter technology allows the user to set the frequency response characteristics of the signal conditioner under program control. For transient tests or tests where time-domain wave shape preservation is important, program the filter characteristic to PULSE mode. The PULSE mode provides linear phase response, which is required for time-domain wave shape reproduction and outstanding transient response with low overshoot and ringing. For frequency domain analysis, selecting the FLAT filter characteristic will result in outstanding transfer function flatness and a sharp, selective filter response. FLAT/PULSE filter technology is available on all Precision Filters’ strain and bridge conditioners.

28000 Bridge and Strain Conditioners

Dual Mode Constant Voltage & BCC Excitation

Precision’s line-up of quad-channel conditioners provides the versatility to condition a wide variety of constant voltage excited sensors including full bridges and sensors that require precise bridge completion. Use the balanced constant current excitation technology to measure 2 or 4-wire dynamic or static strain gage measurements. Choose the full-featured high performance 28144 card, the 28124 card for multiple filtered/wideband outputs or the 28114 for the best value.

Dual Mode Constant Voltage & BCC Excitation Conditioners Common Features:

4-channels/card, 64 channels/system
Balanced programmable constant current or constant voltage excitation w/automatic bridge balance/transducer zero suppress
On-the-fly report of measured transducer excitation, resistance, open/short and leakage to ground

Programmable bridge completion (120 ohms, 350 ohms, 1k ohms), configuration (1, 2, 4-arms)
Programmable 5,000 step shunt calibration
Programmable 2/4-wire constant current mode
Programmable AC/DC input coupling

28144 4-Channel Wideband Transducer Conditioner

Choice of 4 or 8-pole FLAT/PULSE low-pass filters or 8-pole band-pass filters
Over 2,000 unique cutoff frequency settings from 1 Hz to 204.6 kHz
Low noise, high CMRR amplification from x1/16 to x8192 with 0.05% resolution
REZCOMP™ technology to extend frequency response of accelerometer, unsteady pressure and microphone sensor measurements

View the 28144 Specification Sheet >

28124 4-Channel Wideband Transducer Conditioner

4-pole FLAT/PULSE low-pass filters
Over 2,000 unique cutoff frequency settings from 1 Hz to 102.3 kHz
Low noise, high CMRR amplification from x1/16 to x8192 with 0.05% resolution
AC Shunt Calibration for frequency response evaluation of bridge-based sensors

View the 28124 Specification Sheet >

28114 4-Channel Transducer
Conditioner

4-pole FLAT/PULSE low-pass filters
Five programmable cutoffs to 100 kHz
Amplification from x1/16 to x1024 with 0.05% resolution

View the 28114 Specification Sheet >

Bridge Conditioners with Voltage Excitation

Where applications call for high performance, high channel-density bridge conditioning, the 28108 and 28118 octal filter/amplifiers with constant voltage excitation deliver low-noise and DC stability for either AC or DC bridge-based sensor or low-level voltage measurements.

Bridge Conditioners with Voltage Excitation Common Features:

8-channels/card, 128-channels/system
Balanced programmable constant voltage excitation
6-wire + shield transducer interface
Automatic bridge balance

Transducer suppress up to 10V of DC bias
4-pole FLAT/PULSE low-pass filters w/filter bypass
Test Modes: Test-bus, Short, Zero-Excitation, Excitation Monitor

28108 4-Channel Bridge Conditioner

255 programmable cutoff frequency settings
25 kHz filtered or 100 kHz “wideband” bandwidth
Low noise, high CMRR amplification from x1/16 to x8192 with 0.05% resolution

View the 28108 Specification Sheet >

28118 4-Channel Bridge Conditioner

5 programmable cutoff frequency settings from 100 Hz to 30 kHz
30 kHz filtered or 190 kHz “wideband” bandwidth
Programmable amplification from x1/16 to x1,024 with 0.05% resolution

View the 28118 Specification Sheet >

Dynamic Strain with Current Excitation

Measurements of dynamic strain with PFI’s balanced constant current technology are much less susceptible to EMI pickup and lead resistance desensitization that plague single-ended constant current topologies.

28458 Dynamic Strain Conditioners Features:

8-channels/card, 128-channels/system
Balanced programmable constant current excitation with 20 V compliance
2-wire + shield transducer interface
4-pole FLAT/PULSE low-pass filters w/filter bypass
5 programmable cutoff frequency settings
100 kHz filtered or 190 kHz “wideband” bandwidth

Programmable amplification from x1/16 to x1024 with 0.05% resolution
On-the-fly report of measured transducer excitation resistance and leakage to ground
Sensor open and short detection
Test Modes: Test-bus, Short, Zero-Excitation

View the 28458 Specification Sheet >

Bridge and Strain Conditioner Card Selection Guide

Card	28144	28114	28124	28108	28118	28458
Type	AC/DC Voltage, Bridge, Static Strain, Dynamic Strain	AC/DC Voltage, Bridge, Static Strain, Dynamic Strain	AC/DC Voltage, Bridge, Static Strain, Dynamic Strain	AC/DC Voltage, Bridge, Static Strain	AC/DC Voltage, Bridge, Static Strain	AC Voltage, Dynamic strain
Channels/ Card	4	4	4	8	8	8
Applicable Transducer	Static or dynamic strain, pressure, RTD, load, accel, AC/DC filter/amp, any bridge type sensor	Static or dynamic strain, pressure, RTD, load, accel, AC/DC filter/amp, any bridge type sensor	Static or dynamic strain, pressure, RTD, load, accel, AC/DC filter/amp, any bridge type sensor	Static strain, pressure, RTD, load, accel, AC/DC filter/amp, any full bridge type sensor	Static strain, pressure, RTD, load, accel, AC/DC filter/amp, any full bridge type sensor	Dynamic strain, AC/DC filter/amp
Interface	2-10 Wire Constant Voltage w/ Programmable Bridge Completion, Shunt Cal, 2/4 Wire Constant Current	2-10 Wire Constant Voltage w/ Programmable Bridge Completion, Shunt Cal, 2/4 Wire Constant Current	2-10 Wire Constant Voltage w/ Programmable Bridge Completion, Shunt Cal, 2/4 Wire Constant Current	2 to 6 wire w/ Shield	2 to 6 wire w/ Shield	2 wire w/ Shield
Excitation	Constant Voltage: 0 to 20.475V; Balanced Constant Current: 0 to 20.475mA	Constant Voltage: 0 to 20.475V; Balanced Constant Current: 0 to 20.475mA	Constant Voltage: 0 to 20.475V; Balanced Constant Current: 0 to 20.475mA	Constant Voltage: 0 to 20.475 V	Constant Voltage: 0 to 20.475 V	Balanced Constant Current: 0,5,10,15,20 mA
Bandwidth	500 kHz	190 kHz	250 kHz	100 kHz	190 kHz	190 kHz
Gain	x1/16 to x8192 w/ 0.05% Resolution	x1/16 to x1024 w/ 0.05% Resolution	x1/16 to x8192 w/ 0.05% Resolution	x1/16 to x8192 w/ 0.05% Resolution	x1/16 to x1024 w/ 0.05% Resolution	x1/16 to x1024 w/ 0.05% Resolution
Filter	4-Pole Low-Pass with optional REZCOMP, 8-Pole Low-Pass or 8-Pole Band-Pass	4-poles; FLAT/PULSE Low-Pass	4-poles; FLAT/PULSE Low-Pass	4-Pole; FLAT/PULSE Low-Pass	4-Pole, FLAT/PULSE Low-Pass	4-Pole; FLAT/PULSE Low-Pass
Cutoff Frequencies	FLAT: 2 Hz to 204.6 kHz PULSE: 1 Hz to 102.3 kHz	FX02: 300, 1k, 3k, 10k, 30 kHz*	FLAT: 2 Hz to 204.6 kHz PULSE: 1 Hz to 102.3 kHz	FLAT: 100 Hz to 25.5 kHz PULSE: 50 Hz to 12.75 kHz	FX02: 300, 1k, 3k, 10k, 30 kHz*	FX02: 300, 1k, 3k, 10k, 30 kHz*
Outputs	Single ended with Ground Sense	Single ended with Ground Sense	(3) Buffered Prog WB/Filtered SE Outputs per channel w/ Ground Sense	Single-ended or Differential Output (Option T)	Single-ended or Differential Output (Option T)	(2) Buffered Single-Ended Outputs per Channel
					Single-ended or Differential Output (Option T)	(2) Buffered Single-Ended Outputs per Channel

* Custom cutoff frequencies are available. Please consult factory.