CHIP SOLUTIONS FOR THE NEW GENERATION OF DIGITAL LOAD CELLS (DLC)
At the 2010 Inter-weighing Trade Show Acam presented the "DLC 2.0" concept which was about the more convenient and simpler production and temperature adjustment procedure of digital load cells in comparison to the existing workflow. At the 2011 Inter-weighing Trade Show in Shanghai, we took the concept further: thanks to PS09 and its integrated temperature unit a further simplification of the sensor can be done. For example, an only half-bridge based sensor can be used without any further external compensation resistor since the temperature compensation for gain and offset drift can be done by employing the chip's internal temperature unit.
Together with the previously existing high-end solution based on PS081 a whole range of Digital Load Cell types are feasible to build with PICOSTRAIN chip solutions now:
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DLC-TYPE 1: LOW-COST OIML 3000
Features:
DLC-TYPE 2: OIML 6000
Features:
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DLC-TYPE 3: HIGH-END
Features:
ELECTROMAGNETIC INTERFERENCE (EMI):
All the DLC types introduced here were tested on a prototype-basis towards EMI (10V/m) and showed very good results. Thanks to the design of a digital load cell in general (electronics encapsulated in the load cell body) the interference level always stays well within 1e of the relevant specification. Therefore a DLC is a good solution for electromagnetically noisy environments. (See figures below.)
DLC DEVELOPMENT KIT
For an easy entry into DLC design and a fast development acam provides a dedicated digital load cell PCB. The PCB comes together with an entire development kit, which also includes one load cell already equipped with the PCB to show full functionality by ‘plug-and-play’, but there is also a separate PCB to connect your own sensor.
The PCB offers many possibilities for evaluation and design-in, e.g. it is equipped with an external EEPROM for program development and several types of sensors can be connected, e.g. a half-bridge, a classical Wheatstone bridge or the PICOSTRAIN full-bridge.
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RESULT IN ΜV @ 10V/M
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RESULT IN DIVISIONS @ 10V/M
| Description | Version | Size | Download |
|---|---|---|---|
| Datasheet PS09 Vol. 2: CPU - Single-chip solution for strain gauges | V1.0 | 8.9MB | DB_PS09_Vol2_en.pdf |
| Datasheet PS09 Vol. 1: General Data and Front-end Description | V1.0 | 1.8MB | DB_PS09_Vol1_en.pdf |
| Datasheet PS09 Eval System: Evaluation Kit for PS09 | V0.1 | 7.2MB | DB_PS09-EVA_en.pdf |
| Datasheet PS09: DLC Evaluation Kit for PS09 | V0.1 | 4.8MB | DB_PS09-DLC-EVA_en.pdf |
| Datasheet PS081: Enhanced Single-chip solution for | V0.9 | 7.5MB | DB_PS081_en.pdf |
| Datasheet PS081 Eval System: Evaluation kit for PS081 | V0.1 | 5.4MB | DB_PS081-EVA_en.pdf |
| Datasheet PS021: PICOSTRAIN front-end for strain gauge sensors | 870kB | DB_PS021_en.pdf | |
| Datasheet PS021 Eval System: Evaluation system for PS021 | 6.6MB | DB_PSA21_en.pdf | |
| Datasheet ALCS350-V2: Load cell simulator | V0.1 | 1.6MB | DB_ALCS350-V2_en.pdf |
| Datasheet PicoProg081: Production Programmer for PS081 | V0.4 | 1.8MB | DB_PicoProg081_en.pdf |
| Description | Version | Size | Download |
|---|---|---|---|
| Application Note 030: PS09: Using PICOSTRAIN with piezoresistive sensors | V0.0 | 657k | AN030_en.pdf |
| Application Note 025: PS081: EMI Countermeasures for a Digital Load Cell | V1.0 | 1.9MB | AN025_en.pdf |
| Application Note 023: PS081: Design Guideline for Building a Solar Body Scale | V1.3 | 4MB | AN023_en.pdf |
| Application Note 022: PS081: Design Guideline for Building a Solar Kitchen Scale | V1.3 | 4MB | AN022_en.pdf |
| Application Note 021: General: Compensation of gain error for uncompensated load cells | V0.1 | 658kB | AN021_en.pdf |
| Application Note 018: PS08: Metrological investigations of PS08, Determining Zero Drift and Gain Drift | V1.0 | 2.8MB | AN018_en.pdf |
| Application Note 012: General: Strain gage wiring with PICOSTRAIN | 97kB | AN012_en.pdf | |
| Product Report 0909: PS081: ESD reliability report | V1.0 | 240kB | PR0909_en.pdf |
| Description | Version | Size | Download |
|---|---|---|---|
| White Paper 004: PS081: How to build Digital Load Cells with PICOSTRAIN conveniently | V1.0 | 5.2MB | WP004_en.pdf |
| White Paper 003: PS08: Millikelvin Resolution with only a few Microampere | V1.0 | 1.1MB | WP003_en.pdf |
| White Paper 002: PS08 / PS081: How to lower gain and offset drift of a load cell | V1.1 | 2.8MB | WP002_en.pdf |
| White Paper 001: PS08: Construction guideline for solar driven scales | V2.0 | 6MB | WP001_en.pdf |
| Description | Version | Size | Download |
|---|---|---|---|
| Screencasts PS09: 38:11 min. webcast introduction into the PS09 evaluation kit | - | 27MB | PS09_Evaluation-Software_en.zip |
| Screencasts PS09: 19:01 min. | - | 17MB | PS09_Temp-Compensation-ext-Rspan_en.zip |
| Screencasts PS09: 17:54 min. | - | 17MB | PS09_Temp-Compensation_en.zip |
| Screencasts PS081/PS09: 20:28 / 40:30 min. webcast introducing a new concept for digital load cells | - | 11MB | PS081_DLC-Interweighing_en.zip |
| Screencasts PS08/PS081: 13:36 min. | - | 105MB | PS081_Scaling-of-Result_en.zip |
| Screencasts PS08-EVA-KIT: 23:23 min. movie introducing the PS08 assembler software | - | 78MB | ASM-Screencast_en.zip |
| Description | Version | Size | Download |
|---|---|---|---|
| Software PS09: PS09-EVA-KIT, PICOPROG v2.0 | V2.0 | 281MB | CD-PS09-EVA-PICOV20-XP-WIN7.zip |
| Software PS081: PS081-EVA-KIT, PICOPROG v2.0 | V2.0 | 296MB | CD-PS081-EVA-KIT-PICOV20-XP-WIN7.zip |
| Software PS081: PS081-DLC-KIT, PICOPROG v2.0 | V2.0 | 296MB | CD-PS081-DLC-KIT-PICOV20-XP-WIN7.zip |
| Software PSA021/PS021: PSA021 / PS021-EVA-KIT, COM Port | 99MB | CD-PSA21-EVA-KIT-COM-XP.zip | |
| Software PicoProg V3.0 (V2.0): Driver Installer Stand-Alone | R11 | 5MB | PicoProg_v2_Driver_Installer_Stand-Alone.zip |
| Software National Instruments: | V4.62 | 53MB | visa462runtime.exe |
| Software National Instruments: | V4.1 | 41MB | visa410full.exe |
| Software National Instruments: | V3.2 | 14MB | visa320runtime.exe |
The capacitor is charged to the supply voltage and then discharged through one of the SG resistors. The discharge time down to an arbitrary trigger level is measured with ultra-high precision using a TDC (Time-to-Digital Converter). The discharge time is in the range 100 µs. The TDC unit used
This measuring process is repeated in time-multiplex with both resistors of a half-bridge, using the same capacitor and the same comparator. Calculating the ratio of the results will turn out the absolute values and temperature dependencies of the capacitor and the comparator.
Additional patented circuits and algorithms inside the products compensate for further error sources like the switch-on resistance of the output drivers (Rdson) and the propagation delay of the comparator. The result is very precise, nearly free of gain errors and very stable with temperature. In total
Due to the measuring principle, does not need a full-bridge but a half-bridge is sufficient. The supply of the half-bridge is provided directly by the circuits. There is no need for a separate supply of the SG.
Thanks to the pulsed drive easily
The measuring principle is showing a new approach to strain gage (SG) measurement. Contrary to the Wheatstone bridge, where the variation of resistance is transformed into a variation of voltage, solutions transfer it into a high-precision time interval measurement. For this purpose the SG resistors are connected to a capacitor, forming a low-pass filter.
Metal strain gages (SG) change their value with mechanical deformation, especially a variation in length. The strain e designates the relative variation in length of the SG:
Strain (e) = dL/L
Common SG
e(max) = 1000 µ (1000 x 10-6 or 0.1 %).
The ratio of the resistance variation to the length variation is designated K-factor or strain gain.
For metal SG the K-factor is
If the SG is connected in the manner of a Wheatstone bridge, this corresponds to a maximum signal output voltage of 2 mV/V. The resistance of common metal strain gauges is typically 350 Ohm or 1000 Ohm. The maximum variation in resistance and therefore the effective measurement range is within 0.7 Ohm to 2 Ohm. This small variation must be resolved according to the measurement task. The range of the resolution needed is very wide. It is between 10 ENOB (e.g. for pressure sensors) and 18 ENOB (e.g. calibrated scales). In the upper range the precision of the measurement has to be:
Resolution : 2000 ppm/218 = 0.008 ppm eff.
or 26.9 ENOB referenced to the full resistance.
The typical measurement rates are in between
2 - 8 Hz (e.g. scales) and
4 - 10 kHz (e.g. fast pressure sensors).
| Type | Part number | Package | RoHS | Shipping package |
|---|---|---|---|---|
| PS09: | ||||
| PS09 | MNR 1783 | Dice | Yes | Waffle pack |
| PS09FN | MNR 1840 | QFN40 | Yes | |
| PS09-EVA-KIT | MNR 1785 | PCB | Yes | |
| PS09-DLC-EVA | MNR 1927 | PCB | Yes | |
| PS081: | ||||
| PS081 | MNR 1615 | Dice | Yes | Waffle pack |
| PS081FN | MNR 1612 | QFN56 | Yes | |
| PS081-EVA-KIT | MNR 1525 | PCB | Yes | |
| PS021: | ||||
| PS021 | MNR 1002 | TQFP48 | Yes | Tray |
| PS021FN | MNR 1001 | QFN48 | Yes | Tray |
| PSA21-STD | MNR 984 | PCB | Yes | |
| PSA21-WSB | MNR 985 | PCB | Yes | |
| PSA21mini-STD | MNR 990 | PCB | Yes | |
| PSA21mini-WSB | MNR 991 | PCB | Yes | |
| PicoProg: | ||||
| PicoProg Uni System V2.0 | MNR 1723 | PCB | Yes |
ADVANTAGE 1
Extremely low current consumption for your complete bridge sensor system
The ultra-low power PICOSTRAIN measuring principle shows an extremely low overall current consumption of the total system. It is possible to reduce the power consumption by a factor 10 to 20 compared to conventional AD-Converter solutions.
ADVANTAGE 2
One solution suits
PICOSTRAIN allows
ADVANTAGE 3
Reduced overall system costs
PICOSTRAIN reduces or saves the costs of the power supply. Power plugs will be replaced by batteries, batteries will be reduced in size. In many
ADVANTAGE 4
New products that could not be done up to now
There are new product options mainly due to the low current consumption and low operating voltage. First to mention are solar driven applications.
ADVANTAGE 5
Improve your Quality and lower your production cost
PICOSTRAIN offers unique possibilities to simplify the production of your bridge sensor and to improve its quality. The bridge offset can be simply adjusted by setting a register, gain drift can be reduced through software correction of Rspan. This method is more precise than with standard solutions. At the same time costly mechanical trimming,