Vernier Tech Info Library TIL #1952

Question

Can I use Vernier BTA sensors with a different A-to-D converter?

Answer

Our analog (BTA) sensors are normally used with our inexpensive and easy to use interfaces. There are many options, see: http://www.vernier.com/mbl/ . In those cases, you just plug in the sensor, use our software, the sensor is automatically calibrated, and you start taking data. If you want to write your own software, but use our analog sensors, the easiest way to do it is to use one of our interfaces, and start with the sample code at http://www.vernier.com/diy . This is made especially easy if you use LabVIEW.

If you want to use one of our sensors with a different analog-to-digital converter, you can probably do it, but it will be a lot more work. Our BTA sensors produce a voltage output, usually in the range of 0 to 5 volts. You will need to deal with several issues:

- Making the connection: We use BTA connectors on analog sensors. The pinout is at http://www.vernier.com/probes/specs/pinout.html . Our product, Analog Proto Board Connector, order code BTA-ELV, $10.00 , might help you make the connections. One nice thing about this device is that it has built in the 15k resistor that we use to complete the voltage divider circuit which we use on our TMP-BTA and STS-BTA sensors.

Note that we use the 0 to 5 volt connection for all of our analog sensors, except VP-BTA, which is not really a sensor at all (it is just connecting wires). The -10 to +10 volt line is not connected to anything, in general.

- Supplying power: All our sensors require +5.0 Volt power supply. The Ground line also needs to be connected.

- Calibration: Most of our sensor are linear in calibration (voltage vs signal), so calibration is fairly easy. The calibration slope and intercept that we use are usually in the user's guide that comes with the sensor or can be loaded from our web site. For example, the pH user's guide can be download at:
http://www.vernier.com/probes/ph-bta.html

The sensors that are not linearity are:
Temperature probes TMP-BTA and STS-BTA: These are thermistors which we put into a voltage divider circuit and read the voltage at the midpoint. The voltage is related to the temperature by the Steinhart-Hart equation.

Ion selective electrodes have complex calibration curves.

Our Wide-Range Temperature probe (WRT-BTA) has a quadratic calibration curve.

As mentioned above, we provide the slopes and intercepts that we use for standard calibrations on some of the user�s guides for our sensors. You might use these slopes and intercepts, but that is only correct if the following are true:
-The input resistance of your interface is high
- The power supply voltage you provide to the sensor is at 5.00 volts and well regulated.

In general, you probably should do a calibration by taking voltage readings under different conditions.

Created by: dvernier on February 18 2009
Last updated by: jhopkins on December 29 2009