In the last decades the digital load cell (DLC) was a niche product. This is because the production is elaborate and expensive, mainly because of the high efforts for doing the temperature compensation. It is quite difficult to reach a good quality in regards of temperature gain and offset drift which is required by legal specifications such as OIML or NTEP. Indeed, the workflow for making a digital load cell is similar to making an analog one, but setting the digitization on top. Unfortunately, there is only little room left for automation and a simple production.

This is exactly where PICOSTRAIN comes into the game: thanks to our advanced temperature compensation WITHOUT mechanical trimming, the workflow can be simplified.

MAKE "DLC 2.0"

On the basis of existing production processes, the PICOSTRAIN introduces possibilities to make the workflow easier – the production gets simpler and the quality higher. The key point of the new workflow is that you can wholly mount your load cell with electronics BEFORE doing the temperature compensation. There is no need to adjust the load cell manually, the adjustment is done by the chip internally and can be easily automated that way.

        ILLUSTRATION 1                                                                     ILLUSTRATION 2

(click to enlarge)

(click to enlarge)

This leads to a number of advantages, such as:

  • a simpler, more effective and reliable production process
  • higher quality to new adjustment method. Reach specifications like OIML 6000 easier than nowadays
  • a full automatic adjustment of gain and zero drift without mechanical trimming
  • more flexible use of DLCs in standard scales – easier design and better EMC behavior
  • low current consumption and low self heating thanks to the measurement principle
  • easier replacement of the DLC due to intrinsically calibrated unit

Saving cost and effort come automatically with this approach and it allows to think about the digital load cell as the successor of the analog load cell in a way that it makes sense in both – technical and commercial aspects!


In April 2010 Acam exhibited on the largest trade show for weighing solutions in China. The trade show was held in Chansha in the Hunan province from 22nd to 24th of April. We introduced the concept of how to build digital load cells more conveniently in the future. Therefore we had several live demonstrations of DLCs and also held a presentation about this topic in the plenum of the China Weighing Instrument Association (CWIA). Remains of the trade show are a White Paper dedicated to the topic of digital load cells and also the recording of the presentation. The Whitepaper and the recording of the presentation is available in the right column of this page together with further information.

Datasheet PS09 Vol. 2:
CPU - Single-chip solution for strain gauges
Datasheet PS09 Vol. 1:
General Data and Front-end Description
Datasheet PS09 Eval System:
Evaluation Kit for PS09
Datasheet PS09:
DLC Evaluation Kit for PS09
Datasheet PS081:
Enhanced Single-chip solution for weigh scales
Datasheet PS081 Eval System:
Evaluation kit for PS081
Datasheet PS021:
PICOSTRAIN front-end for strain gauge sensors
Datasheet PS021 Eval System:
Evaluation system for PS021
Datasheet ALCS350-V2:
Load cell simulator
Datasheet PicoProg081:
Production Programmer for PS081
Application Note 030:
PS09: Using PICOSTRAIN with piezoresistive sensors
Application Note 025:
PS081: EMI Countermeasures for a Digital Load Cell
Application Note 023:
PS081: Design Guideline for Building a Solar Body Scale
Application Note 022:
PS081: Design Guideline for Building a Solar Kitchen Scale
Application Note 021:
General: Compensation of gain error for uncompensated load cells
Application Note 018:
PS08: Metrological investigations of PS08, Determining Zero Drift and Gain Drift
Application Note 012:
General: Strain gage wiring with PICOSTRAIN
Product Report 0909:
PS081: ESD reliability report
White Paper 004:
PS081: How to build Digital Load Cells with PICOSTRAIN conveniently
White Paper 003:
PS08: Millikelvin Resolution with only a few Microampere
White Paper 002:
PS08 / PS081: How to lower gain and offset drift of a load cell
White Paper 001:
PS08: Construction guideline for solar driven scales
Screencasts PS09:
38:11 min. webcast introduction into the PS09 evaluation kit
Screencasts PS09:
19:01 min. webcast shows how to do a correct temperature compensation of a load cell using PS09 using the load cell's Rspan
Screencasts PS09:
17:54 min. webcast shows how to do a correct temperature compensation of a load cell using PS09 using the PS09 internal temperature sensor
Screencasts PS081/PS09:
20:28 / 40:30 min. webcast introducing a new concept for digital load cells
Screencasts PS08/PS081:
13:36 min. webcast shows how to do a correct scaling of the HB0 measurement result
Screencasts PS08-EVA-KIT:
23:23 min. movie introducing the PS08 assembler software
Software PS09:
Software PS081:
Software PS081:
Software PSA021/PS021:
PSA021 / PS021-EVA-KIT, COM Port
Software PicoProg V3.0 (V2.0):
Driver Installer Stand-Alone
Software National Instruments:
NI VISA runtime engine for Windows 7
Software National Instruments:
NI VISA runtime engine for Windows Vista
Software National Instruments:
NI VISA runtime engine for Windows XP
PICOSTRAIN Measurement Principle

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 have a typical single-shot resolution of less than 20 ps.

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 each single measurement is made of 8 discharge/charge cycles to solve this compensation task.

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. Also the reference voltage is not required.

Thanks to the pulsed drive easily controls the current through the whole system and, even more important, reduces the current consumption to re-markably less than comparable ADC systems.

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.

Measurement Principle
(click to enlarge)

PicoStrain Background : Measurement Task

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 have a maximum strain of typical

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.

dR/R = K x dL/

For metal SG the K-factor is typically of value 2. The maxim variation of the SG resistance is then given as:

dR(max)/R = e(max) x K = 2000 ppm

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).

TypePart numberPackageRoHS compl.Shipping package
PS09MNR 1783DiceYesWaffle pack
PS09FNMNR 1840QFN40Yes
PS081MNR 1615DiceYesWaffle pack
PS081FNMNR 1612QFN56Yes
PS021MNR 1002TQFP48YesTray
PS021FNMNR 1001QFN48YesTray
PSA21mini-STDMNR 990PCBYes
PSA21mini-WSBMNR 991PCBYes
PicoProg Uni System V2.0MNR 1723PCBYes

picostrain advantages


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.


One solution suits to (nearly) all applications, from low cost up to highest precision

PICOSTRAIN allows to build systems with 1.500 ... 150,000 peak to peak divisions (at 2 mV/V strain) and update rates up to 1 kHz. One and the same chip covers the requirements of many applications, just by variation of your software.


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 applications a single coin cell battery may last for 10 years under normal operation. The number of external components is far below the usual.


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. Also 1.55 V silver-oxide batteries are possible although with some restrictions (e.g. re-programming). The measurement quality is impressive even at those low voltages and it might be difficult to find something comparable in the market.


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, wich is still common practice, becomes redundant.