Field service engineers require a variety of load cells spanning the various ranges required to calibrate their customers’ systems. They may also need the assortment to conduct a variety of force measurements for a particular testing application. The challenge begins when the engineer needs to alter the load cell which is linked to his instrument before he can continue. When the multi axis load cell is linked to the instrument, the proper calibration factors must be set up 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 a bad parameters, as well as worse, corrupting the existing calibration data, can cause erroneous results and costly recalibration expenses. Instrumentation that automatically identifies the load cell being mounted on it and self-installing the correct calibration details are optimal.
What exactly 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 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 level of standardization. Even when using the data templates, it is really not guaranteed that different vendors of TEDS-compliant systems will interpret what data is put into the electronic templates in the same manner. More importantly, it is really not apparent that the calibration data that is required inside your application will be backed up by a particular vendor’s TEDS unit. You have to also be sure that you have a means to write the TEDS data to the TEDS-compatible load cell, either through a TEDS-compatible instrument that has both TEDS-write and TEDS-read capabilities, or by using various other, likely computer based, TEDS data writing system.
For precision applications, such as calibration systems, it ought to be noted that calibration data that is stored in the stress cell is identical regardless of what instrument is linked to it. Additional compensation for the 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 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 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 can also be supported. This can be a critical advantage in precision applications such as field calibration services.
With all the TEDS-Tag system, a tiny and inexpensive electronic identification chip is put within the cable that extends from your load cell or it can be mounted within the cell housing. This chip has a unique electronic serial number that can be read by the ESL Model 4215 or CellMite to distinguish the cell. The cell is then linked to the unit along with a standard calibration procedure is conducted. The instrument automatically stores the calibration data in the unit itself together 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 correct calibration data. True plug-and-play operation is achieved. Using this system the calibration data can automatically include compensation for your particular instrument in order that high precision matched systems could be realized. Moreover, when the cell is transferred to another instrument, that instrument will recall the calibration data that it has stored internally for that load cell. The ESL instruments can store multiple load cell calibration entries. This way, 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 easily provided by distributors or from ESL. The chip is quite small, making it easy 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 connected to load cells via a DB9 connector with identical pin outs. The electronic identification chip does not interfere with the cell’s signals. Pin 3 of the DS2401 will not be used and can be shut down if desired. Simply connecting pins 1 and 2 through the DS2401 to pins 8 and 7, respectively, of 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 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 into the DB9 connector. The DS2401 is soldered across DB9 pins 7 and 8, and fits inside 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 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 application, the cable adapter is actually positioned in series using the load cell cable before it really is plugged into the ESL instrument. Additionally it is 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 could 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 each in-line adapter. This might be useful, as an example, in case a precision 6-point linearization of the load cell is required by two different operating ranges of the identical load cell.
Given that the load cell continues to be transformed into a TEDS-Tag unit, it could be attached 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 regular calibration procedure is performed to initialize the cell’s calibration data in the instrument. The ESL instruments support a number of industry standard calibrations including mV/V, shunt, 2-point, or multiple-point calibration. The instrument then automatically detects the existence of the force transducer and matches it using its calibration data. Out of this point forward, the program is completely plug-and-play.