Bridge-based sensors are are a common type of resistive sensor that produce a very small voltage drop. Load cells, strain gauges, pressure sensors, and piezoelectric sensors are all examples of sensors that usually operate in this way. In order to measure these tiny voltage changes, you need a Wheatstone bridge input. The Wheatstone Bridge Phidget uses a high-resolution ADC to to read up to two of these signals and plugs into any VINT port. See the "Compatible Products" tab for a list of VINT Hubs.
This board is equipped with a 24-bit analog to digital converter, resulting in accurate measurements at resolutions as high as 59.6 µV/V. The bridge gain can be changed in software to 1, 2, 64, or 128, allowing you to get the best resolution for the range of the sensor you use. An error event will be launched whenever the measurement value saturates, so your program can dynamically change the gain when necessary.
|Number of Bridge Inputs||2|
|Bridge Voltage Resolution||59.6 nV/V|
|Sampling Interval Max||60 s/sample|
|Sampling Interval Min||20 ms/sample|
|Bridge Current Max||50 mA|
|Input Voltage Limit Min||Ground + 0.25V DC|
|Input Voltage Limit Max||5V Supply - 0.25V DC|
|Current Consumption Min||25 μA|
|Current Consumption Max||*bridge current plus 1.5 mA|
|Recommended Wire Size||16 - 26 AWG|
|Operating Temperature Min||-40 °C|
|Operating Temperature Max||85 °C|
* - The extra 1.5mA of current consumption varies depending on the data interval selected. See the technical section of the User Guide for details. Additional gain-sensitive specifications can also be found there.
|Bridge Input||VoltageRatioInput||0 - 1|
|VoltageRatioInput||Visual Basic .NET||Windows||Download|
|Date||Board Revision||Device Version||Comment|
|June 2017||0||104||Product Release|
Welcome to the DAQ1500 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 DAQ1500!
In order to demonstrate the functionality of the DAQ1500, 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 DAQ1500.
After plugging the DAQ1500 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:
|Gain||Resolution (nV/V)||Noise Floor (nV/V)||Output Range (mV/V)|
Load cells are pressure sensors that can be used with the DAQ1500. 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 DAQ1500. 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 DAQ1500 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 DAQ1500 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.
The bridge inputs can be powered down, reducing power consumption with DAQ1500 sensors, and useful for reducing heating of sensors, which can introduce errors.
The amount of current consumed by the DAQ1500 varies based on the data interval you select:
Use the following equation to approximate the relationship between current consumption and data interval (up to a maximum data interval of 60000ms):
This figure is the no-load current, so to estimate total current consumption, you'll need to measure the current consumption at a known data interval so you can determine the offset, which should be no higher than 50mA.
This Phidget is a smart device that must be controlled by a VINT Hub. For more information about VINT, have a look at the VINT Primer. You can use a Phidget Cable to simply and easily connect the two devices. Here's a list of all of the different VINT Hubs currently available:
You can connect up to four load cells to the DAQ1500 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 DAQ1500 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|
Use a Phidget cable to connect this device to the hub. You can solder multiple cables together in order to make even longer Phidget cables, but you should be aware of the effects of having long wires in your system.