Load Sensor – Common Questions..

Field service engineers require many different load cells spanning the different ranges needed to calibrate their customers’ systems. They may also need the assortment to conduct a variety of force measurements for the testing application. The challenge begins when the engineer has to alter the load cell which is linked to his instrument before he can continue. When the 3 axis load cell is connected to the instrument, the correct calibration factors must be installed in the instrument.

Avoiding user-error is actually a major challenge with manual data entry or with requiring the engineer to select from a database of stored calibration parameters. Loading the incorrect parameters, or even worse, corrupting the current calibration data, can lead to erroneous results and costly recalibration expenses. Instrumentation that automatically identifies the burden cell being attached to it and self-installing the appropriate calibration data is optimal.

What exactly is Transducer Electronic Datasheet? A Transducer Electronic Data Sheet (TEDS) stores transducer identification, calibration and correction data, and manufacturer-related information in a uniform manner. The IEEE Instrumentation and Measurement Society’s Sensor Technology Technical Committee developed the formats which include common, network-independent communication interfaces to connect transducers to microprocessors and instrumentation systems.

With TEDS technology, data may be stored inside of a memory chip that is certainly installed on the inside of a TEDS-compliant load cell. The TEDS standard is complicated. It specifies a huge number of detailed electronic data templates with many amount of standardization. Even while using the data templates, it is far from guaranteed that different vendors of TEDS-compliant systems will interpret what data enters into the electronic templates in the same manner. More importantly, it is really not apparent that the calibration data that is needed in your application will be backed up by a particular vendor’s TEDS unit. You must also be sure that you have a way to write the TEDS data to the TEDS-compatible load cell, either through a TEDS-compatible instrument which has both TEDS-write and TEDS-read capabilities, or through the use of a few other, likely computer based, TEDS data writing system.

For precision applications, including calibration systems, it also need to be noted that calibration data that is kept in the burden cell is the same no matter what instrument is connected to it. Additional compensation for the instrument itself is not included. Matched systems where a field service calibration group could be attaching different load cells to several instruments can present a difficulty.

Electro Standards Laboratories (ESL) has evolved the TEDS-Tag auto identification system which retains the attractive feature of self identification based in the TEDS standard but can be implemented simply on any load cell and, when linked to the ESL Model 4215 smart meter or CellMite intelligent digital signal conditioner, becomes transparent to the user. Multiple load-cell and multiple instrument matched pair calibrations can also be supported. This may be a critical advantage in precision applications like field calibration services.

Using the TEDS-Tag system, a small and cheap electronic identification chip is positioned in the cable that extends from your load cell or it can be mounted within the cell housing. This chip includes a unique electronic serial number that may be read through the ESL Model 4215 or CellMite to recognize the cell. The cell will then be connected to the unit as well as a standard calibration procedure is conducted. The instrument automatically stores the calibration data inside the unit itself combined with the load cell sensor identification number through the microchip. Whenever that cell is reconnected towards the instrument, it automatically recognizes the cell and self-installs the correct calibration data. True plug-and-play operation is achieved. Using this system the calibration data can automatically include compensation for the particular instrument to ensure that high precision matched systems could be realized. Moreover, if the cell is moved to another instrument, that instrument will recall the calibration data it has stored internally for the load cell. The ESL instruments can store multiple load cell calibration entries. This way, multiple load cells can form a matched calibration set with multiple instruments.

Any load cell can be easily made in to a TEDS-Tag cell. The electronic identification chip, Dallas Semiconductor part number DS2401, is readily offered by distributors or from ESL. The chip is extremely small, making it easy to squeeze into a cable hood or cell housing.

Both the ESL Model 4215 smart strain gauge indicator as well as the CellMite intelligent digital signal conditioner are attached to load cells by way of a DB9 connector with identical pin outs. The electronic identification chip does not interfere with the cell’s signals. Pin 3 in the DS2401 is not really used and will be cut off if desired. Simply connecting pins 1 and two from your DS2401 to pins 8 and 7, respectively, from the ESL DB9 connector will enable plug-and-play operation.

When you use off-the-shelf load cells, it is often useful to locate the DS2401 in the hood in the cable. The cell features a permanently mounted cable that protrudes from the cell housing. At the conclusion of the cable, strip back the insulation from your individual wires and solder the wires into the DB9 connector. The DS2401 is soldered across DB9 pins 7 and 8, and fits inside the connector’s hood. For a few dollars in parts and a simple cable termination procedure, you have taken a regular load cell and transformed it into a TEDS-Tag plug-and-play unit.

For applications in which access to the load cell and cable is restricted, an in-line tag identification module could be simply constructed. A straight through in-line cable adapter can incorporate the DS2401 electronic tag chip. In this particular application, the cable adapter is actually positioned in series with all the load cell cable before it is plugged into the ESL instrument. Additionally it is possible to use this technique in applications where different calibrations might be required on the same load cell. The ifegti may have a single load cell and instrument, but may change which calibration is auto-selected simply by changing the in-line cable adapter. Since each cable adapter includes a different tag identification chip, the ESL instrument will associate a different calibration data set with each in-line adapter. This can be useful, for example, in case a precision 6-point linearization of the load cell is required in two different operating ranges of the identical load cell.

Since the load cell has been transformed into a TEDS-Tag unit, it can be attached to the ESL Model 4215 smart strain gauge indicator or even a CellMite intelligent digital signal conditioner. The 1st time it is connected, a standard calibration procedure is carried out to initialize the cell’s calibration data inside the instrument. The ESL instruments support a variety of industry standard calibrations including mV/V, shunt, 2-point, or multiple-point calibration. The instrument then automatically detects the actual existence of the force sensor and matches it using its calibration data. Out of this point forward, the system is entirely plug-and-play.