Field service engineers require a number of load cells spanning the different ranges needed 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 has to alter the load cell that is connected to his instrument before he could continue. When the new cell is linked to the instrument, the appropriate calibration factors need to be set up in the Load Cell.
Avoiding user-error is really a major challenge with manual data entry or with requiring the engineer to select from a database of stored calibration parameters. Loading a bad parameters, as well as worse, corrupting the present calibration data, can result in erroneous results and costly recalibration expenses. Instrumentation that automatically identifies the load cell being attached to it and self-installing the correct calibration information 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 which include common, network-independent communication interfaces to connect transducers to microprocessors and instrumentation systems.
With TEDS technology, data can 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 some amount of standardization. Even when 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 manner. More importantly, it is not apparent the calibration data that is needed in your application will likely be backed up by a certain vendor’s TEDS unit. You have to also make certain you have a way to write the TEDS data to the TEDS-compatible load cell, through either a TEDS-compatible instrument that has both TEDS-write and TEDS-read capabilities, or with the use of some other, likely computer based, TEDS data writing system.
For precision applications, like calibration systems, it ought to be noted that calibration data which is kept in the load cell is the same regardless of what instrument is attached to it. Additional compensation for the Torque Transducer is not included. Matched systems in which a field service calibration group might be attaching different load cells to various instruments can present a difficulty.
Electro Standards Laboratories (ESL) has created the TEDS-Tag auto identification system which retains the attractive feature of self identification based in the TEDS standard but may be implemented simply on any load cell and, when connected to the ESL Model 4215 smart meter or CellMite intelligent digital signal conditioner, becomes transparent for the user. Multiple load-cell and multiple instrument matched pair calibrations are also supported. This can be a critical advantage in precision applications such as field calibration services.
With all the TEDS-Tag system, a tiny and cheap electronic identification chip is put inside the cable that extends from your load cell or it can be mounted inside the cell housing. This chip has a unique electronic serial number that may be read by the ESL Model 4215 or CellMite to recognize the cell. The cell will then be attached to the unit along with a standard calibration procedure is conducted. The instrument automatically stores the calibration data inside the unit itself combined with the unique load cell identification number from your microchip. Whenever that cell is reconnected towards the instrument, it automatically recognizes the cell and self-installs the appropriate calibration data. True plug-and-play operation is achieved. With this system the calibration data can automatically include compensation for the particular instrument in order that high precision matched systems may be realized. Moreover, in the event the cell is moved to another instrument, that instrument will recall the calibration data which it has stored internally for your 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 be easily made right 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 extremely small, rendering it simple to match a cable hood or cell housing.
Both the ESL Model 4215 smart strain gauge indicator and the CellMite intelligent digital signal conditioner are linked to load cells using a DB9 connector with identical pin outs. The electronic identification chip fails to interfere with the cell’s signals. Pin 3 in the DS2401 is not used and will be shut down if desired. Simply connecting pins 1 and 2 from your DS2401 to pins 8 and 7, respectively, from the ESL DB9 connector will enable plug-and-play operation.
When using off-the-shelf load cells, it is usually easy to locate the DS2401 inside the hood from the cable. The cell includes a permanently mounted cable that protrudes through the cell housing. At the end of the cable, strip back the insulation from the 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 dollars in parts and a simple cable termination procedure, you may have taken a typical load cell and transformed it in to a TEDS-Tag plug-and-play unit.
For applications where access to the load cell and cable is fixed, 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 application, the cable adapter is in fact placed in series with the load cell cable before it really is connected to the Load Cell. It is also possible to make use of this technique in applications where different calibrations could be required on the same load cell. An individual may mbssap one particular 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 another calibration data set with every in-line adapter. This can be useful, as an example, when a precision 6-point linearization from the load cell is needed by two different operating ranges the exact same load cell.