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 the testing application. The challenge begins when the engineer needs to alter the load cell that is attached to his instrument before he can continue. When the 3 axis load cell is connected to the instrument, the appropriate calibration factors have to be placed in the instrument.
Avoiding user-error is really a major challenge with manual data entry or with requiring the engineer to pick from a database of stored calibration parameters. Loading the incorrect parameters, as well as worse, corrupting the present calibration data, can lead to erroneous results and costly recalibration expenses. Instrumentation that automatically identifies the load cell being connected to it and self-installing the appropriate calibration data is 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 including common, network-independent communication interfaces to connect transducers to microprocessors and instrumentation systems.
With TEDS technology, data could be stored on the inside of a memory chip that is installed inside of a TEDS-compliant load cell. The TEDS standard is complicated. It specifies a huge number of detailed electronic data templates with a few degree of standardization. Even when using the data templates, it is not guaranteed that different vendors of TEDS-compliant systems will interpret what data goes into the electronic templates in the same manner. Moreover, it is really not apparent that this calibration data that is required within your application will be backed up by a certain vendor’s TEDS unit. You need to also be sure that you have a method to write the TEDS data in to the TEDS-compatible load cell, either through a TEDS-compatible instrument which includes 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 should also be noted that calibration data that is certainly kept in the stress cell is identical whatever instrument is linked to it. Additional compensation for the instrument itself is not included. Matched systems where a field service calibration group may be attaching different load cells to various instruments can present a problem.
Electro Standards Laboratories (ESL) has created the TEDS-Tag auto identification system which retains the attractive feature of self identification found in the TEDS standard but may 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 for the user. Multiple load-cell and multiple instrument matched pair calibrations are also supported. This may be a critical advantage in precision applications such as field calibration services.
With the TEDS-Tag system, a little and inexpensive electronic identification chip is put inside the cable that extends from your load cell or it may be mounted in the cell housing. This chip includes a unique electronic serial number which can be read by the ESL Model 4215 or CellMite to identify the cell. The cell will be connected to the unit as well as a standard calibration procedure is carried out. The instrument automatically stores the calibration data inside the unit itself combined with the weight sensor identification number through 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 the particular instrument to ensure that high precision matched systems can 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 that 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 easily offered by distributors or from ESL. The chip is very small, which makes it easy to match a cable hood or cell housing.
Both 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 affect the cell’s signals. Pin 3 in the DS2401 will not be used and may be shut down if desired. Simply connecting pins 1 and 2 from the 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 convenient to locate the DS2401 in 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 from the individual wires and solder the wires in to the DB9 connector. The DS2401 is soldered across DB9 pins 7 and 8, and fits inside the connector’s hood. For a couple of dollars in parts as well as a simple cable termination procedure, you have taken a regular load cell and transformed it right into a TEDS-Tag plug-and-play unit.
For applications in which accessibility 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 really placed in series using the load cell cable before it is actually connected to the ESL instrument. It is also easy to use this technique in applications where different calibrations might be required on the same load cell. The ifegti could have a single load cell and instrument, but may 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 a different calibration data set with every in-line adapter. This can be useful, for instance, when a precision 6-point linearization of the load cell is needed in two different operating ranges the exact same load cell.
Given that the load cell continues to be transformed into a TEDS-Tag unit, it can be connected 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 conducted 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 presence of the force transducer and matches it using its calibration data. From this point forward, the system is entirely plug-and-play.