instruNet

The instruNet voltage input terminals (often labeled "Vin(+)" or "Vin(-)") can directly connect to a variety of sensors, with instruNet software returning values in native engineering units (e.g. degrees Celsius, strain, Volts, Amps, ohms). This requires wiring the sensor to the instruNet hardware in the appropriate manner, and then configuring the instruNet software for your particular sensor, as described in the following steps:

1) Physically Wire your Sensor to instruNet hardware
The first step is to physically wire your sensor to the instruNet hardware, per the Sensor Setup Instructions. For example, to connect a J Thermocouple, one would attach the positive lead of the thermocouple to the instruNet Vin+ terminal, and the negative lead to the Vin- terminal. The input terminals are protected against over voltage and electrostatic discharge, therefore it is not always necessary to power off network devices (e.g. Model 100) while wiring sensors, although turning power off is recommended as a good safety practice. If you do power OFF your network, please use the following sequence:

Power OFF powered devices connected to the Network
Power OFF Computer
Configure network cables, sensors, and devices
Power ON Computer
Power ON powered devices connected to the Network

2) Tell the instruNet software which Sensor is connected
Set the Sensor popup in the Hardware settings area of the Probe dialog to the correct Sensor (e.g. Volts, J Thermocouple, etc). If you are not sure how to set this field, please consult Sensor Setup Instructions.

To set the Sensor popup, one would:

Open the instruNet World window by launching the Windows "instruNet World Win32.exe" or Macintosh "instruNet World Mac" application program (e.g. double-click on its icon).
Click on the Network tab at the bottom of the window to select the network page.
Click on the name of your channel in the left-most column to open the Probe dialog.
Select Hardware in the Settings popup menu.
Select the desired sensor in the Sensor popup menu, as illustrated in the previous figure.

3) Tell the instruNet software how the Sensor is wired
Set the Wiring popup in the Hardware settings area of the Probe dialog to the correct Wiring (e.g. Single-Ended, Differential, Bridge, Voltage Divider, etc). For guidance, please consult Sensor Setup Instructions. Recall that the chosen wiring popup must match your actual physical hardware wiring.

4) Set the appropriate constants as required

Set the fields in the Constants settings area as needed. This involves selecting Constants in the Setting popup, and then setting specific Constants fields as noted in Sensor Setup Instructions. For example, to measure a resistance instruNet needs to know the value of an external shunt resistor "Rshunt", in ohms, and the value of the excitation voltage "Vout", in volts, as illustrated above. This would involve setting the Rshunt and Vout Constants fields to correspond to your actual wiring. instruNet software would then automatically return an amplitude in "ohms" units after measuring the voltage at the Vout terminal, measuring the voltage between the Vin+ and Vin- terminals, and calculating the realtime Runknown.

5) Select the appropriate input voltage range
Set the Range popup in the Hardware Settings area as needed. This selects a voltage range that is used by instruNet. If the voltage exceeds a bound, then the bound is returned by the software. For example, if you input 2V and the range is +/- 1V then instruNet will return 1Volt. The resolution and accuracy of the measured signal increases when the range is reduced. For example, with the Model 100, the voltage accuracy is 15uV in the +/-10mV range, and 1.5mV in the +/- 5V range with 1ms of integration. Some sensors require a specific voltage range, or only allow one range. For example, the range with thermocouples is always in the neighborhood of +/- 100mV.

6) Set the Integrate field
Set the Integrate field in the Hardware Settings area as needed. This selects the duration that the signal is averaged before instruNet returns one number. For example, if you choose 0.016666 seconds (one 60Hz line cycle), it will return the average signal value over a period of 0.016 sec. This is helpful at reducing noise for signals acquired at slow sample rates (e.g. to integrate 0.016 seconds worth of data the sample rate must be greater than 0.016 seconds per point, or slower that 60samples/second). Each hardware device offer different Integrate options. For details, see Sample Rate Vs Integration Vs. Noise.

7) Select the appropriate Analog Filter
Set the analog Low Pass filter popup in the Hardware Settings area as needed (e.g. off, 40Hz, 4KHz). Each hardware device offers different analog low pass filter options (not all devices support hardware analog filtering). Low pass filters cause high frequencies to be rejected, while low frequencies are passed. Visually, the signal becomes "smoother". To see the effects of various filters, view the digitized signal at the bottom of the probe dialog, after making different selections (you might not be able to do this until you are further along in the set up process).

8) Set your Digital filters as needed
If you need to do a digital low pass, high pass, band pass, or band stop filter on your digitized waveform, please set the fields in the filter Settings areas (e.g. Low Pass, High Pass) as desired. Digital filters are run on the waveform post acquisition, and only effect digitized waveforms (not single values read by instruNet). Please refer Setting Digital Filters for an expanded discussion of this powerful feature.

9) Consult the Sensor Reference for specifics
Carefully implement the Sensor Setup Instructions for your particular sensor. Different sensors require different range, filter, and constants settings; and care should be taken to insure accurate results.

10) Check your Work
To check your work, view the incoming signal, in realtime, at the bottom of the Probe dialog.

This display shows the sensor's value, in realtime, in native engineering units (e.g. Volts, Amps, degrees Celsius, strain) based on your software settings and external hardware wiring. The numerical value displayed at the bottom right is the actual real time value being read by instruNet. The plot shows the digitized version of your sensor value vs. time. The horizontal scale of this display is determined by the Pts Per Scan, No. of Scans, Scan Mode, Horiz Scale, and Sample Rate fields within the global Setup dialog (i.e. press the Record tab at the bottom of the instruNet World window, and then press the Setup button at the top). For details on how these work, please consult Working with the Voltage Inputs. To adjust the vertical scale of the probe display, select Display in the Setting popup, and then set the Display Max and Display Min fields to the desired engineering units values that correspond to the top and bottom of the display (e.g. set 1 and -1 to view a signal that varies from -1V to 1V). Press the Enter button to cause the new settings to take effect, and then view the updated display.

11) If your Sensor is not working, Fix it !
Listed below are several debugging hints for channels that are returning "bad" results:

a. Check that you have the correct channel
To check that you have the correct channel, and that it is being digitized by the software, view the probe dialog display as you disconnect one wire from your sensor. The value printed in the dialog lower right corner should change, to indicate that your displayed value is in some way connected to that wire. Also, if you touch the input terminal with your finger, you should notice some slight variation since your body acts as an antenna and causes radio stations, and such, to drive the input terminal (due to its high input impedance).

b. Check that instruNet is correctly measuring the voltage
At any time, you can set the Sensor popup to Volts, and set the Wiring popup to Vin+ - Vin- to cause instruNet to measure the voltage between the Vin+ and Vin- terminals. The measured voltage appears in the Probe dialog lower right. You can then check this against a volt meter that is placed in parallel between the Vin+ and Vin- terminals. Remember to set the Range popup if your signal is "clipping" on a bound. To measure the voltage between your Vin screw terminal (Vin+ or Vin-) and ground, you would do the same thing, yet select Vin - Gnd in the Wiring popup.

c. Check the engineering units calculations
If your voltage looks good, yet the returned engineering units value looks bad, then pull out a calculator (or better yet, a spreadsheet) and run your constants and known values into the equations listed in the Sensor Reference to check the processing of these numbers. Perhaps one of the fields in the Constants settings area is not set correctly.

d. Make sure you do not exceed the maximum input voltage
Make sure you are not exceeding the maximum input voltage, with respect to the Gnd terminal. To check this, measure the voltage between the Vin+ (or Vin-) terminal and the Gnd terminal with a Volt Meter. For example, in the Model 100, this voltage must not be less than -5V or greater than +5V. Exceeding a maximum typically does not cause damage unless it is very large (e.g. greater than +/- 20V).

e. Check your ground connections
If the ground between the instruNet device and your signal source is unstable, then connecting a wire between the instruNet Gnd terminal, and your signal source ground might help (e.g. attach a wire, or 1Kohm resistor, between the GND and Vin(-) terminals). Alternatively, if the instruNet Gnd is tied to the ground of your signal source, and these are at different voltages with respect to Earth ground, then current will flow between them. This current will cause voltage drops and subsequently may induce weird effects -- breaking this ground connection might help. The best way to determine what helps is to try different things (e.g. hold a wire between two grounds) and observe what happens in the display at the bottom of the Probe dialog.

g. Recheck your work
Recheck your hardware wiring and software settings.

12) Save your work.
To save the current configuration of instruNet (i.e. the settings displayed in the Network page and accessed via the Probe dialog), press the Network tab at the bottom of the window to select the Network page, and then press the Save button at the top of the window to save the settings to disk. A file save dialog appears, and it is here that you must specify a file name and file location (remember where you put it).

To check your saved settings: exit instruNet world, re-enter instruNet (e.g. launch Windows "instruNet World Win32.exe" or Macintosh "instruNet World Mac"), press the Network tab at the bottom of the window to select the Network page, press the Open button at the top of the window, select your saved settings file (this will load your save settings), click on the channel that you just set up, and then view the realtime display at the bottom of the Probe dialog.

Alternatively, one could press the Store button to save the settings directly to a preferences file in the operating system folder, and then press the Restore button, at a later date, to restore them. The advantage of Save/Restore is the user does not need to specify a file name or file location; whereas the disadvantage is the saved file is overwritten the next time someone presses Store.