View source for 1046 User Guide

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<metadesc>The PhidgetBridge 4-Input measures the output from a load cell and connects to a USB port. You can connect up to 4 load cells or strain gauges. </metadesc>
[[Category:UserGuide]]
==Part 1: Setup==
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== Part 2: Using Your Phidget ==

===About===
The PhidgetBridge reads up to four load cells, strain gauges or Wheatstone Bridge-based sensors. The Phidget reports results as a voltage ratio. To convert from voltage ratio to a quantity like weight or force, see the '''Calibration Guide''' in the Advanced Topics section.

===Explore Your Phidget Channels Using the Control Panel===

You can use your Control Panel to explore your Phidget's channels.

'''1.''' Open your Control Panel, and you will find the following channels:

[[Image:1046_Panel.jpg|link=|center]]

'''2.''' Double click on a channel to open an example program. Each channel belongs to the '''Voltage Ratio Input''' channel class:
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{{UGC-Entry|Voltage Ratio Input (Bridge Input):| Read data from a load cell
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In your Control Panel, double click on "Bridge Input":
[[Image:1046-VoltageRatio.jpg|800px|center|link=]]}}

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== Part 4: Advanced Topics and Troubleshooting ==

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{{UGC-Entry|Connecting Your Strain Gauge or Load Cell|
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Load cells are force sensors that can be used with the 1046. To get useful data from load cells, they will need to be calibrated. Fortunately this is a simple process outlined in our guide on [[Calibrating Load Cells]]

For more information, see our [[Load Cell Guide]].

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.}}

{{UGC-Entry|Measuring RTDs|
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While we used to recommend using this product to measure RTDs, we now recommend using the {{ProductListLink|TMP1200|RTD Phidget}}.
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{{UGC-Entry|Calibration|
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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.

For sensors with a linear response, like load cells, look at our guide on [[Calibrating Load Cells]].
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{{UGC-Entry|Choosing a Gain Value|
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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.


{{1046-Gain-table}}


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.
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{{UGC-Entry|Measurement Considerations|
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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. }}

{{UGC-Entry|The number I’m getting back from the 1046 is really small|
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Load cells output a small voltage proportional to the amount of strain they are currently experiencing. The rated output for most load cells at full load is in the order of millivolts, so when you’re only straining the load cell at a fraction of its full load, you will get very small values. In order to convert to meaningful units like grams or newtons, you need to [[Calibrating_Load_Cells|calibrate]] the load cell.}}

{{UGC-Entry|The DataInterval doesn't match the actual rate of incoming data|
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Due to limitations in the hardware, the actual DataInterval must be a multiple of 8. If you try to set a DataInterval that isn't a multiple of 8, the library will automatically round down to the nearest multiple of 8. So if you set DataInterval to 31, you'll end up with an actual interval of 24ms. 
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{{UGC-Entry|I'm getting an "Invalid" error if I try to get data right after opening the channel|
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The 1046_1 has an improved calibration routine which takes approximately 3 seconds to complete when the channel is first opened. You should have your program wait a few seconds before polling for data, or you can catch the exception and retry until the request succeeds. If you want to get data as early as possible, use an [[Using Events|event handler]] instead of polling.
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