Binsfeld Engineering Inc. :: Tech Info - TorqueTrak 10K

TorqueTrak 10K Common Topics

A) FEATURES & BENEFITS: Measure real torque on almost any shaft without machine modifications with the TorqueTrak 10K. With 14 bit resolution and 500Hz frequency response, the TorqueTrak 10K provides exceptionally accurate data collection, transmitting data 20 feet or more from the shaft to the receiving antenna. The 9V battery-powered TX10K-S Transmitter operates at any one of 16 channels in the 902-925MHz RF band, allowing simultaneous data collection from multiple sensors with multiple systems. Changing the Channel or Gain settings of the TX10K-S from up to 10 feet away prior to shaft rotation is as easy as clicking a button on the handheld RM10K Remote Control. The RX10K Receiver supplies the data transmitted by the TX10K-S in three ways: an analog Voltage Output signal (+/-10VDC), a digital data stream via RS-232 serial connection, and as a visual representation of the Voltage Output on the two-line LCD display. Measuring torque has never been easier!
B) SYSTEM INSTALLATION: Installing the TorqueTrak 10K is simple. Once the strain gage is installed and wired (see the next topic on Strain Gage Installation), secure the TX10K-S Transmitter and BH10K Battery Housing (with 9V battery inserted) to the shaft with a generous amount (5-10 wraps) of the fiberglass-reinforced strapping tape provided. Connect the gage and power wires to the TX10K-S terminals. Position the Receiver Antenna connected to the RX10K Receiver to achieve the best signal strength. Prior to machine startup, adjust the Channel and Gain settings on the TX10K-S with the RM10K Remote Control. Connect your data acquisition equipment to the RX10K and set the AutoZero and other parameter adjustments as desired. You are now ready to measure live torque. Total instrument setup time is roughly one hour not including gage installation.
C) STRAIN GAGE INSTALLATION: Installation of the strain gage is often the most intimidating step in the process. After a little practice, it is a skill that can be quickly mastered. Refer to the step-by-step procedure in the User Manual for a standard full-bridge torque-pattern strain gage, Vishay Micromeasurements Group Part #: CEA-06-250US-350, using the Strain Gage Application Kit, Vishay Part #: GAK-2-200. Strain gages and application kits can be ordered through Binsfeld Engineering Inc. Once the strain gage has been applied, simply solder a piece of 4-conductor ribbon cable provided with the TorqueTrak 10K system to the strain gage as illustrated in the manual. Optionally, if the gage is to be used again over an extended period of time, it can be preserved using a protective polymer coating, Part #: M-Coat J, also available from Vishay. For more information on the strain gage products manufactured by Vishay, refer to their website: www.vishay.com.
D) DATA PROCESSING & DISPLAY: The TorqueTrak 10K system provides data in three ways: an Analog Voltage (+/-10VDC), a digital data stream via RS-232 interface, and a displayed value equivalent to the Voltage Output in millivolts. Since no device fits every user's particular needs or price requirements, Binsfeld Engineering does not supply data acquisition equipment with the TorqueTrak 10K. However, there are many data acquisition solutions commonly available. DATAQ and National Instruments offer both hardware and software for data acquisition. Visit their websites at www.dataq.com and www.ni.com for more information. For long-term data storage, try Data Recorders (Arraycorders) from Graphtec USA: www.westerngraphtec.com. The digital data stream requires a computer with a serial COM port (RS-232). Many computers are no longer supplied with this connection, since USB has become the standard. In this case, a USB-to-Serial/PDA Converter Cable will be required. We recommend IOGEAR Model #: GUC232A (refer to their website: www.iogear.com). The computer's processing speed must be able to accomodate the RX10K data rate of 2,400 samples per second. Next, software will be required to receive, interpret, and store this data. Examples of software of this type are LabVIEW and DASYLab. The digital data protocol is not complex but some programming is required to convert it into useable data. Please see the specification in Appendix A of the User Manual available on this website for more information.
E) ACCURACY & CALIBRATION: Using the TorqueTrak 10K system, you can achieve accuracy better than +/-1% of Full Scale. Accuracy is a function of two primary elements: proper installation of the strain gage and accurate determination of the "sensitivity" of the system. The "system" includes the shaft, strain gage, and the TorqueTrak 10K. Sensitivity is expressed as Torque Input per Voltage Output. This Input-Output relationship is linear throughout the elastic range of the material. The most precise method for determining the sensitivity is performing a true mechanical calibration, often referred to as a deadweight calibration. With this method, a known torque is applied to the shaft (i.e., a known force or weight is applied to the shaft at a known distance from the load to the center of the shaft). Example: A 100-lb load on a 1-foot moment arm creating 100 foot-pounds of torque is applied to the shaft. Observe the change in the Voltage Output. The sensitivity of the system is equal to this Torque Input to Voltage Output ratio. Changing the amount of mass or length of the moment arm can be useful to confirm the sensitivity and linearity of the system. Be careful when using free weights: the perpendicular distance from the load to the shaft will be slightly less once the weight is applied depending on how much the shaft twists. The other, more commonly used, method is by calculation of the Full Scale Torque. Taking the values for Shaft Diameter (this should be accurately measured), Modulus of Elasticity and Poisson Ratio of the shaft material (these can be estimated if unknown but may introduce an uncertainty of as much as +/-3%), the Gage Factor of the strain gages being used (printed on the package), and the TX10K-S Gain setting (based on the peak torque is expected), then the Full Scale Torque result for a given range of strain can be determined. There are two ways to calculate the Full Scale Torque. One is by using the equation in Appendix B of the User Manual, and the other is to use the TT10K Torque Range Calculator in the Tech Info section of this website. For the TorqueTrak 10K, the result of this calculation is the Full Scale Torque that corresponds to a Voltage Output of exactly 10VDC. Sensitivity is equal to this calculated value for Full Scale Torque Input divided by the Full Scale Voltage Output (10VDC).
F) REFERENCE SHUNT RESISTORS: A great calibration feature of the TorqueTrak 10K are the internal Reference Shunt Resistors. There are two precision resistors inside the TX10K-S Transmitter that can be activated individually with the RM10K Remote Control. Activating one of these resistors places it in parallel with one arm of the strain gage to simulate a known amount of strain. For example, at a Gain level of 4000, Reference 1 simulates 20% of the Full Scale Strain and Reference 2 simulates 100%. Strain is proportional to torque, so in this case with a perfectly balanced bridge, a Voltage Output of +2.000VDC (or 20% of the calculated Full Scale Torque) would be expected with Reference 1 activated and +10.000VDC (or 100% of Full Scale Torque) with Reference 2 activated. Based on the actual Voltage Output values, the sensitivity can be recalculated or the System Gain on the RX10K can be adjusted so the Voltage Output equals the expected (calculated) value. This calibration adjustment takes into account deviation in the system due to minor imbalance or imperfection in the strain gage or wiring. The Reference Shunt Resistors can help verify proper scaling of the Voltage Output. (The System Gain is adjustable from 0.25 to 4.0 times the Transmitter Gain). See the User Manual on this website for more information. Another method to check calibration is to apply reference resistors externally at either the terminals for the strain gage or the TX10K-S. The Torque Strain calculator in the Tech Info section of this website can be helpful in determining the actual strain generated based on a given torque value to be simulated and then what resistor value should be chosen in order to simulate this amount of strain/torque. The Voltage Output reading with this resistor applied can then be used in the same way as with the on-board Reference Shunt Resistors to either recalculate the sensitivity or make adjustments to the System Gain.
G) MULTIPLE CHANNELS: A channel is a single data transmission signal from a single sensor, usually a strain gage bonded to the shaft. The TorqueTrak 10K has 16 channels available. Each channel transmits data at a different frequency within the 902 to 925MHz RF band. The RX10K Receiver can process only one data signal at a time and provides only one common output signal (delivered in three ways). Each system only comes with one TX10K-S Transmitter and one RX10K Receiver, so in order to collect data simultaneously from more than one gage, you will need as many systems as there are gages (up to 16), and each will need to be on a different channel to prevent "crosstalk" interference. To reduce the chance of interference, space the channels out as much as possible. For instance, if you have four sensors, Channels 1, 6, 11, and 16 would be the preferred setup as compared with 1, 2, 3, and 4. If simultaneous data is not required, a single RX10K can be used to receive the data transmission from up to 16 TX10K-S Transmitters. The user would simply toggle from one channel to the next using the keypad on the RX10K. However, complications with this method may include the need for different Gain settings on the various transmitters that affect the AutoZero and other calibration and scaling adjustments. Even with the same Gain setting, gage offsets will most likely not all be the same. Depending on the type of analysis being conducted, these details may not be a problem, but it is good to be aware of the issues up front.
H) SMALL SHAFTS, LOW CLEARANCE: When a given shaft is small, 1" (25mm) or less, balance may be an issue. With a battery installed, the Battery Holder is within a gram of the TX10K-S Transmitter without the antenna that simply screws into an embedded connector. Mount the units 180 degrees form one another. On very small shafts, (less than 0.5" or 13mm), mounting even the strain gage can be difficult. The TX10K-S can transmit short distances (up to 6 feet or 2 meters from the Receiver Antenna) without the antenna installed. This can also allow the TX10K-S to be installed in areas with very little clearance around the shaft.
I) LOW PASS FILTER: The TorqueTrak 10K system has a maximum frequency response of 500Hz. However, this resolution is not always needed or desired. The RX10K Receiver allows the user to select from a range of low pass filters from 250 to as low as 1Hz. This effectively "averages" the torque data, smoothing out high frequency oscillation and noise.
J) RADIO FREQUENCY INTERFERENCE: The TorqueTrak 10K systm is designed to create a dependable wireless link for the transfer sensor data. Since it is a wireless system, it it subject to external influences not present in a hard-wired system. This interference can cause an interruption in the signal transfer from the TX10K-S Transmitter to the RX10K Receiver. This interruption is indicated on the RX10K display as "TX->Rx Data Error" and a 12-volt output. Most devices that generate RF energy will not interfere with the TorqueTrak 10K. However, if they are transmitting on a similar frequency, in close proximity, or emitting very intense RF or electromagnetic energy, interference is possible. Non-intentional RF radiators include computers, instrumentation, and controls such as motors, generators, solenoids, and relays. Another potential source of interference is multipath. This is when radio waves generated by the TX10K-S are reflected by nearby objects and may cause multiple signals to reach the RX10K antenna at the same time. This may degrade the signal or be interpretted as an error. When an interference problem occurs, there are several ways to eliminate or improve the signal reception. Moving the Receiver Antenna is easiest and a good place to start. Typically, the closer the Recieving Antenna is to the TX10K-S, the better the signal strength will be. However, if the problem is due to multipath, moving the antenna further away may help. Another possible solution is to change the channel, moving the transmission out of the interfering RF band. Moving the TX10K-S and Receiver Antenna away from the interference source or reflective surface may also improve signal integrity. Applying one of the filter settings may also help. The filters reduce the error checking since the data is being "averaged", so occassional bad signals that cause an error at 500Hz may be ignored at a lower filter setting.