Field service engineers require many different load cells spanning the numerous ranges necessary to calibrate their customers’ systems. They may also require the assortment to conduct an array of force measurements for a particular testing application. The challenge begins when the engineer needs to change the load cell that is connected to his instrument before he can continue. When the 3 axis load cell is linked to the instrument, the correct calibration factors must be placed in the instrument.
Avoiding user-error is a major challenge with manual data entry or with requiring the engineer to pick from a database of stored calibration parameters. Loading a bad parameters, or perhaps worse, corrupting the present calibration data, can lead to erroneous results and costly recalibration expenses. Instrumentation that automatically identifies the stress cell being attached to it and self-installing the proper calibration data is optimal.
Precisely what 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 that include common, network-independent communication interfaces for connecting transducers to microprocessors and instrumentation systems.
With TEDS technology, data can be stored within a memory chip that is certainly installed inside of a TEDS-compliant load cell. The TEDS standard is complicated. It specifies a large number of detailed electronic data templates with a few degree of standardization. Even while using the data templates, it is far from guaranteed that different vendors of TEDS-compliant systems will interpret what data goes into the electronic templates in the same way. More importantly, it is really not apparent the calibration data that is required within your application will be maintained by a specific vendor’s TEDS unit. You have to also make certain you have a method to write the TEDS data to the TEDS-compatible load cell, through a TEDS-compatible instrument that has both TEDS-write and TEDS-read capabilities, or with the use of various other, likely computer based, TEDS data writing system.
For precision applications, like calibration systems, it ought to be noted that calibration data that is saved in the stress cell is identical regardless of what instrument is connected to it. Additional compensation for the instrument itself is not included. Matched systems where a field service calibration group might be attaching different load cells to different instruments can present an issue.
Electro Standards Laboratories (ESL) has developed the TEDS-Tag auto identification system which retains the attractive feature of self identification found in the TEDS standard but can be implemented simply on any load cell and, when attached 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 will also be supported. This may be a critical advantage in precision applications including field calibration services.
With the TEDS-Tag system, a little and inexpensive electronic identification chip is put in the cable that extends through the load cell or it can be mounted within the cell housing. This chip includes a unique electronic serial number which can be read through the ESL Model 4215 or CellMite to recognize the cell. The cell is then attached to the unit and a standard calibration procedure is conducted. The instrument automatically stores the calibration data in the unit itself together with the load cell sensor identification number from the microchip. Whenever that cell is reconnected to the instrument, it automatically recognizes the cell and self-installs the proper calibration data. True plug-and-play operation is achieved. With this system the calibration data can automatically include compensation for that particular instrument in order that high precision matched systems could be realized. Moreover, in the event the cell is relocated 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. In this way, multiple load cells can form a matched calibration set with multiple instruments.
Any load cell can easily be made in to a TEDS-Tag cell. The electronic identification chip, Dallas Semiconductor part number DS2401, is easily provided by distributors or from ESL. The chip is quite small, rendering it simple to match a cable hood or cell housing.
The ESL Model 4215 smart strain gauge indicator and also the CellMite intelligent digital signal conditioner are connected to load cells using a DB9 connector with identical pin outs. The electronic identification chip does not hinder the cell’s signals. Pin 3 of the DS2401 will not be used and may be cut off if desired. Simply connecting pins 1 and two from your DS2401 to pins 8 and 7, respectively, of the ESL DB9 connector will enable plug-and-play operation.
When utilizing off-the-shelf load cells, it is usually convenient to locate the DS2401 within the hood of the cable. The cell features a permanently mounted cable that protrudes through the cell housing. After the cable, strip back the insulation from your individual wires and solder the wires to the DB9 connector. The DS2401 is soldered across DB9 pins 7 and 8, and fits within the connector’s hood. For a couple of dollars in parts along with a simple cable termination procedure, you may have taken a typical 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 can be simply constructed. A straight through in-line cable adapter can incorporate the DS2401 electronic tag chip. In this application, the cable adapter is really put into series with all the load cell cable before it is actually connected to the ESL instrument. It is also possible to make use of this technique in applications where different calibrations could be required on the same load cell. The ifegti may have a single load cell and instrument, but could change which calibration is auto-selected simply by changing the in-line cable adapter. Since each cable adapter features a different tag identification chip, the ESL instrument will associate an alternative calibration data set with each in-line adapter. This might be useful, for instance, if a precision 6-point linearization of the load cell is necessary in 2 different operating ranges the exact same load cell.
Given that the burden cell has been converted to a TEDS-Tag unit, it could be connected to the ESL Model 4215 smart strain gauge indicator or perhaps a CellMite intelligent digital signal conditioner. The 1st time it is connected, a standard calibration procedure is performed to initialize the cell’s calibration data in 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 presence of the force transducer and matches it using its calibration data. From this point forward, the program is completely plug-and-play.