The PhidgetBridge lets you connect up to 4 un-amplified Wheatstone bridges, such as:
The data rate and gain values can be configured in software.
|API Object Name||Bridge|
|Number of Bridge Inputs||4|
|Bridge Data Rate Min||* 8 ms|
|Bridge Data Rate Max||1000 ms|
|Bridge Input Current Max||± 3 nA|
|Differential Voltage Resolution||24 bit|
|USB Voltage Min||4.5 V DC|
|USB Voltage Max||5.3 V DC|
|USB Speed||Full Speed|
|Current Consumption Min||35 mA|
|Current Consumption Max||500 mA|
|Available External Current||465 mA|
|Input Voltage Limit Min||Ground + 0.25V DC|
|Input Voltage Limit Max||5V Supply - 0.25V DC|
|Recommended Wire Size||16 - 26 AWG|
|Operating Temperature Min||0 °C|
|Operating Temperature Max||70 °C|
|Bridge Input||VoltageRatioInput||0 - 3|
|Date||Board Revision||Device Version||Comment|
|May 2011||0||100||Product Release|
|May 2011||0||101||getLabelString fixed for labels longer than 7 characters|
|February 2014||0||102||Various fixes: usb stack, gain switching, bad values after enable|
Welcome to the 1046 user guide! In order to get started, make sure you have the following hardware on hand:
Next, you will need to connect the pieces:
Now that you have everything together, let's start using the 1046!
In order to demonstrate the functionality of the 1046, the Phidget Control Panel running on a Windows machine will be used.
The Phidget Control Panel is available for use on both macOS and Windows machines. If you would like to follow along, first take a look at the getting started guide for your operating system:
Linux users can follow the getting started with Linux guide and continue reading here for more information about the 1046.
After plugging the 1046 into your computer and opening the Phidget Control Panel, you will see something like this:
The Phidget Control Panel will list all connected Phidgets and associated objects, as well as the following information:
The Phidget Control Panel can also be used to test your device. Double-clicking on an object will open an example.
Double-click on the Voltage Ratio object, labelled Bridge Input, in order to run the example:
General information about the selected object will be displayed at the top of the window. You can also experiment with the following functionality:
We have observed a 1.5% difference between a 1x gain and an 8x gain. This may require that each system (1046 and sensors) be calibrated as a whole. For maximum accuracy, decide on, and keep with a chosen gain before calibrating the system.
Expensive sensors will ship with a certificate of calibration specifying, often in mv/V, how the sensor responds to stimulus. Less expensive will have to be calibrated, which requires having at least two points where you know accurately what is being measured. In the case of weight measurement, this would be a known force or weight.
Record the output from the 1046 at one known point, and at a second known point. It helps if the two values are reasonably far apart. Use the values to make a linear equation to convert the 1046 output in V/V (called X) to the appropriate unit you are measuring (called Y). Two calibration coefficients (a,b) set the slope and offset for the calibration: (Y = aX + b). It’s possible to use more than two points, if available.
The C# VoltageRatioInput example shows how to do a 2-point calibration and apply the coefficients programmatically.
We report the measured voltage in a ratiometric unit known as V/V. This is how the maximum range of sensors that use strain gauges is usually specified. V/V is the output value in V of the measured sensor, scaled for a 1V sensor supply voltage. This value will correspond to the physical quantity that the sensor is measuring, regardless of the actual voltage supplied to the sensor.
|1||119 nV/V||± 1000 mV/V|
|8||14.9 nV/V||± 125 mV/V|
|16||7.45 nV/V||± 62.5 mV/V|
|32||3.72 nV/V||± 31.25 mV/V|
|64||1.86 nV/V||± 15.625 mV/V|
|128||0.93 nV/V||± 7.8125 mV/V|
When choosing the Gain setting, it's best to use the highest gain possible that can still measure the full range of your sensor. For an individual unit, you can apply the maximum stimulus to the sensor, and ensure the voltage ratio reported is well within the range for the gain setting you have chosen. If many units are being deployed, it’s best to consult the data sheet for the strain gauge and look for maximum offset.
Some wheatstone bridges, most often those produced from silicon and used in pressure sensors, will have a very wide offset, and large manufacturing variation in the offset. This will restrict the gain to lower settings, particularly if the application must support a number of deployed systems with the expected variation. Fortunately, the very high precision electronics used in the 1046 means that in many application, higher gain is not necessary to get adequate accuracy and resolution.
Load cells are pressure sensors that can be used with the 1046. For more information, see our Load Cell Primer.
If no documentation is available for your strain gauge, it’s possible to use a multimeter to determine how to connect it, provided there are no electronics in the sensor. First, measure resistance between the 4 wires. There are 6 combinations - two combinations will have a resistance 20-40% higher than the other four. Choose one of these high-resistance combinations, and wire it into 5V and G on the 1046. Connect the other two wires into +/-. Apply a load, if the V/V responds in the opposite way to your expectations, flip the +/- wires.
The 1046 is designed to measure voltages as a ratio of the supply voltage - it’s not practical to make measurements of absolute voltages with this product.
For maximum accuracy, all wires from the 1046 to the sensor should be the same length and thickness. Changes in temperature will change the resistance of the wires - if they are all the same, the errors will cancel out.
Each bridge input can be powered down, reducing power consumption with 1046 sensors, and useful for reducing heating of sensors, which can introduce errors.
Using a slower sampling rate will reduce the noise in the measurements dramatically. The noise figures are specific to individual applications and sensors. The lowest noise level achievable is 5nV/V RMS.
A Wheatstone bridge is the classic method of measuring unknown resistances, and requires three resistors of known values. It uses the current in each leg of the bridge to create a voltage differential between both voltage dividers. Using the voltage differential and the three known resistors, the resistance of the fourth resistor can be determined.
To determine the resistance of the RTD, the following formula can be used:
Where is the Bridge Value given by the PhidgetBridge (in mV/V) , and , and are the resistances of the known resistors.
The alternate method requires only two resistors. This reduces the amount of error that can be introduced into the system due to resistor tolerances. A voltage is applied to the two resistors and the RTD in series. The voltage drop across the RTD is measured. Using the voltage drop and the values of the two resistors, the resistance of the RTD can be determined.
To determine the resistance of the RTD, the following formula can be used:
Where is the Bridge Value given by the PhidgetBridge (in mV/V) , and and are the resistances of the known resistors.
In order to get the highest accuracy from the RTD, consider the following:
You can connect up to four load cells to the PhidgetBridge in order to measure the amount of strain in the cell. See the product page or manual for your load cell to learn how to hook it up. We have a variety of types available to measure different types of strain: shear, compression, and tension. See the Load Cell Primer for more information.
|Image||Part Number||Price||Sensor Type||Weight Capacity Max||Creep||Zero Balance||Cell Repeatability Error Max||Cell Non-Linearity Max||Cell Hysteresis Max|
|3132_0||$6.00||Shear Load Cell||780 g||1.6 g/hr||± 11.7 g||± 390 mg||390 mg||390 mg|
|3133_0||$7.00||Shear Load Cell||5 kg||5 g/hr||± 75 g||± 2.5 g||2.5 g||2.5 g|
|3134_0||$7.00||Shear Load Cell||20 kg||20 g/hr||± 300 g||± 10 g||10 g||10 g|
|3135_0||$7.00||Shear Load Cell||50 kg||50 g/hr||± 750 g||± 25 g||25 g||25 g|
|3136_0||$45.00||Compression Load Cell||50 kg||20 g/hr||± 500 g||± 100 g||100 g||—|
|3137_0||$45.00||Compression Load Cell||200 kg||* 40 g/hr||* ± 2 kg||* ± 200 g||* 400 g||—|
|3138_0||$45.00||Compression/Tension Load Cell||100 kg||—||—||—||—||—|
|3139_0||$7.00||Shear Load Cell||100 g||—||—||± 50 mg||50 mg||50 mg|
|3140_0||$50.00||Compression/Tension Load Cell||500 kg||—||—||—||—||—|
|3141_0||$50.00||Compression Load Cell||1 Mg||—||—||—||—||—|
Strain gauges are ideal for situations where you want to monitor the strain in a material that's already a part of your project. By attaching strain gauges in a strategic way, you can effectively turn a load-bearing member into a custom load cell. You can read strain gauges using the PhidgetBridge by connecting them as described in the Strain Gauge Primer.
|Product||Sensor Properties||Electrical Properties|
|Image||Part Number||Price||Sensor Type||Strain Gauge Mount Type||Resistance Value|
|3142_0||$12.50||Torque Half-bridge Strain Gauge||Steel||(per quarter-bridge) 1 kΩ|
|3143_0||$12.50||Torque Half-bridge Strain Gauge||Aluminum||(per quarter-bridge) 1 kΩ|
|3144_0||$15.00||Half-bridge Strain Gauge||Steel||(per quarter-bridge) 1 kΩ|
|3145_0||$15.00||Half-bridge Strain Gauge||Aluminum||(per quarter-bridge) 1 kΩ|
|3146_0||$17.50||Full-bridge Strain Gauge||Steel||(per quarter-bridge) 1 kΩ|
|3147_0||$17.50||Full-bridge Strain Gauge||Aluminum||(per quarter-bridge) 1 kΩ|
You can protect your board from dust and debris by purchasing an enclosure. An enclosure will also prevent unintentional shorts caused by objects touching the pins on the bottom of the board or any terminal screws.
If you need to use the PhidgetBridge to interface with a platinum RTD or some other wheatstone bridge circuit, you can use these precision resistors for the best measurement accuracy. For details on how to hook up RTDs and bridge circuits, see the technical section of the User Guide.
|Image||Part Number||Price||Resistance Value||Resistance Error Max|
|3175_0||$4.00||1 kΩ||0.1 %|
Use a USB cable to connect this Phidget to your computer. We have a number of different lengths available, although the maximum length of a USB cable is 5 meters due to limitations in the timing protocol. For longer distances, we recommend that you use a Single Board Computer to control the Phidget remotely.