Field service engineers require a number of load cells spanning the various ranges necessary to calibrate their customers’ systems. They may also need the assortment to conduct an array 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 linked to the instrument, the correct calibration factors need to be set up in the instrument.
Avoiding user-error is 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, or even worse, corrupting the existing calibration data, can result in erroneous results and costly recalibration expenses. Instrumentation that automatically identifies the burden cell being mounted on it and self-installing the correct 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 including common, network-independent communication interfaces to connect transducers to microprocessors and instrumentation systems.
With TEDS technology, data may be stored on the inside of a memory chip that is certainly 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 far from guaranteed that different vendors of TEDS-compliant systems will interpret what data is put into the electronic templates in a similar manner. Most importantly, it is really not apparent that this calibration data that is needed within your application will likely be maintained by a specific vendor’s TEDS unit. You must also make certain you have a means to write the TEDS data into the TEDS-compatible load cell, either through a TEDS-compatible instrument that has both TEDS-write and TEDS-read capabilities, or through the use of various 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 saved in the stress cell is the same regardless of what instrument is connected to it. Additional compensation for your instrument itself is not included. Matched systems in which a field service calibration group may be attaching different load cells to several instruments can present an issue.
Electro Standards Laboratories (ESL) has evolved the TEDS-Tag auto identification system which retains the attractive feature of self identification located 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 for the user. Multiple load-cell and multiple instrument matched pair calibrations can also be supported. This can be a critical advantage in precision applications like 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 can be mounted in the cell housing. This chip contains a unique electronic serial number that can be read by the ESL Model 4215 or CellMite to recognize 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 within the unit itself along with the weight sensor identification number from your microchip. Whenever that cell is reconnected for 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 may be realized. Moreover, if the cell is transferred 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 into a TEDS-Tag cell. The electronic identification chip, Dallas Semiconductor part number DS2401, is readily offered by distributors or from ESL. The chip is very small, making it easy to fit into a cable hood or cell housing.
The ESL Model 4215 smart strain gauge indicator and the CellMite intelligent digital signal conditioner are attached to load cells via a DB9 connector with identical pin outs. The electronic identification chip fails to hinder the cell’s signals. Pin 3 of the DS2401 will not be used and will be stop 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 usually 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 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 as well as a simple cable termination procedure, you have taken a standard 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 particular application, the cable adapter is really placed in series with the load cell cable before it is connected to the ESL instrument. It is also easy 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 could 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 an alternative calibration data set with each in-line adapter. This can be useful, as an example, in case a precision 6-point linearization in the load cell is required in two different operating ranges the exact same load cell.
Given that the burden cell has become changed into 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 first time it is connected, a typical calibration procedure is carried out to initialize the cell’s calibration data within the instrument. The ESL instruments support many different 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. Out of this point forward, the program is entirely plug-and-play.