Field service engineers require many different load cells spanning the different 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 must change the load cell which is linked to his instrument before he can continue. When the multi axis force sensor is linked to the instrument, the proper 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 a bad parameters, or even worse, corrupting the current calibration data, can lead to erroneous results and costly recalibration expenses. Instrumentation that automatically identifies the load cell being mounted on it and self-installing the appropriate 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 including common, network-independent communication interfaces to connect transducers to microprocessors and instrumentation systems.
With TEDS technology, data could be stored inside of a memory chip which 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 degree of standardization. Even while using the data templates, it is not guaranteed that different vendors of TEDS-compliant systems will interpret what data is put into the electronic templates in the same way. More importantly, it is really not apparent that the calibration data that is required in your application is going to be maintained by a certain vendor’s TEDS unit. You must also ensure that you have a means to write the TEDS data in to 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 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 that 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 located in the TEDS standard but could 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 towards the user. Multiple load-cell and multiple instrument matched pair calibrations will also be supported. This is often a critical advantage in precision applications such as field calibration services.
Using the TEDS-Tag system, a little and inexpensive electronic identification chip is positioned inside the cable that extends from the load cell or it may be mounted within the cell housing. This chip contains a unique electronic serial number which can be read from the ESL Model 4215 or CellMite to distinguish the cell. The cell will be connected to the unit as well as a standard calibration procedure is conducted. The instrument automatically stores the calibration data inside the unit itself combined with the weight sensor identification number from 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 particular 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 the 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 be easily made into a TEDS-Tag cell. The electronic identification chip, Dallas Semiconductor part number DS2401, is readily available from distributors or from ESL. The chip is extremely small, making it simple to fit into a cable hood or cell housing.
Both ESL Model 4215 smart strain gauge indicator as well as the CellMite intelligent digital signal conditioner are attached 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 in the DS2401 will not be used and may 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 utilizing off-the-shelf load cells, it is usually convenient to locate the DS2401 inside the hood in the cable. The cell comes with a permanently mounted cable that protrudes from the cell housing. After the cable, strip back the insulation through the individual wires and solder the wires to the DB9 connector. The DS2401 is soldered across DB9 pins 7 and 8, and fits in 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 right into a TEDS-Tag plug-and-play unit.
For applications where accessibility load cell and cable is fixed, an in-line tag identification module may 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 all the load cell cable before it really is connected to the ESL instrument. Additionally it is possible to make use of 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 can change which calibration is auto-selected by just 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 might be useful, for example, if a precision 6-point linearization in the load cell is required in two different operating ranges the exact same load cell.
Now that the load cell has been transformed into a TEDS-Tag unit, it may be linked to the ESL Model 4215 smart strain gauge indicator or perhaps a CellMite intelligent digital signal conditioner. The very first time that it is connected, a regular calibration procedure is carried out to initialize the cell’s calibration data inside 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 presence of the force sensor and matches it with its calibration data. From this point forward, the program is completely plug-and-play.