Field service engineers require a variety of load cells spanning the different ranges needed to calibrate their customers’ systems. They may also require the assortment to conduct a wide range of force measurements for the testing application. The challenge begins when the engineer must change the load cell which is connected to his instrument before he can continue. When the multi axis force sensor is linked to the instrument, the proper calibration factors must be installed 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 the wrong parameters, or perhaps worse, corrupting the current calibration data, can lead to erroneous results and costly recalibration expenses. Instrumentation that automatically identifies the burden cell being connected to it and self-installing the proper calibration details are optimal.
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 may be stored within a memory chip that is installed within a TEDS-compliant load cell. The TEDS standard is complicated. It specifies a large number of detailed electronic data templates with a few amount of standardization. Even while using the data templates, it is really not guaranteed that different vendors of TEDS-compliant systems will interpret what data enters into the electronic templates in the same manner. Most importantly, it is not apparent the calibration data that is needed inside your application is going to be backed up by a certain vendor’s TEDS unit. You must also make certain you have a means to write the TEDS data in to the TEDS-compatible load cell, through either a TEDS-compatible instrument that has both TEDS-write and TEDS-read capabilities, or through the use of some other, likely computer based, TEDS data writing system.
For precision applications, such as calibration systems, it should also be noted that calibration data which is stored in the load cell is the same regardless of what instrument is linked to it. Additional compensation for that instrument is not included. Matched systems in which a field service calibration group could be attaching different load cells to various 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 will also be supported. This is often a critical advantage in precision applications including field calibration services.
Using the TEDS-Tag system, a little and inexpensive electronic identification chip is positioned in the cable that extends from the load cell or it could be mounted within the cell housing. This chip includes a unique electronic serial number that may be read from the ESL Model 4215 or CellMite to distinguish the cell. The cell is then linked to the unit as well as a standard calibration procedure is carried out. The instrument automatically stores the calibration data within the unit itself combined with the load cell sensor identification number from your microchip. Whenever that cell is reconnected for the instrument, it automatically recognizes the cell and self-installs the proper calibration data. True plug-and-play operation is achieved. With this particular system the calibration data can automatically include compensation for that particular instrument in order that high precision matched systems may be realized. Moreover, in the event the cell is transferred to another instrument, that instrument will recall the calibration data which it has stored internally for the load cell. The ESL instruments can store multiple load cell calibration entries. In this manner, multiple load cells can form a matched calibration set with multiple instruments.
Any load cell can easily be made into a TEDS-Tag cell. The electronic identification chip, Dallas Semiconductor part number DS2401, is readily provided by distributors or from ESL. The chip is quite 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 connected to load cells by way of a DB9 connector with identical pin outs. The electronic identification chip will not hinder the cell’s signals. Pin 3 from the DS2401 will not be used and will be shut down if desired. Simply connecting pins 1 and 2 from your DS2401 to pins 8 and 7, respectively, in the ESL DB9 connector will enable plug-and-play operation.
When you use off-the-shelf load cells, it is often easy to locate the DS2401 inside the hood of the cable. The cell comes with a permanently mounted cable that protrudes from your cell housing. At the end of the cable, strip back the insulation through the individual wires and solder the wires into the DB9 connector. The DS2401 is soldered across DB9 pins 7 and 8, and fits in the connector’s hood. For a few dollars in parts and a simple cable termination procedure, you may have taken a regular load cell and transformed it into a TEDS-Tag plug-and-play unit.
For applications by 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 placed in series with the load cell cable before it really is plugged into the ESL instrument. It is also possible to utilize this technique in applications where different calibrations may be required on the same load cell. The ifegti may have a single load cell and instrument, but can change which calibration is auto-selected by simply changing the in-line cable adapter. Since each cable adapter includes 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, in case a precision 6-point linearization of the load cell is necessary in two different operating ranges of the identical load cell.
Given that the stress cell continues to be changed into a TEDS-Tag unit, it could be linked to the ESL Model 4215 smart strain gauge indicator or perhaps a CellMite intelligent digital signal conditioner. The first time that it is connected, a typical calibration procedure is carried out to initialize the cell’s calibration data within 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 featuring its calibration data. Out of this point forward, the device is totally plug-and-play.