Vernier Software and Technology
Vernier Software & Technology
Tech Info Library

Why is my sensor reading different in MINDSTORMS than on the NXT screen?

This answer assumes all of the following:

• You are using our LEGO NXT adapter with a LEGO NXT Robotics Kit.
• You are using LEGO Mindstorms software after importing our Vernier Sensor block.

There are three ways to display data: LEGO Mindstorms NXT Programming, LEGO Mindstorms NXT Data Logging, or on the NXT device itself.

• If your NXT is connected to your computer, the sensor readings will be displayed in the Configuration Panel of the LEGO MINDSTORMS LEGO Programming screen, which is located in the lower, left-hand corner. The Vernier Sensor block must be selected.
• In LEGO MINDSTORMS LEGO Data Logging, you must click the Download and Run button (the green arrow) to begin data collection. The data will be displayed live graphically.
• You can also display the reading on the NXT.

If the readings on the computer and on the NXT do not agree, there may be a Vernier Sensor.cal file on your NXT that is causing the problem. This file is created when you use the Zero/Calibrate functionality in the Vernier Sensor Block. When this file is created, it resides on the NXT and is used forever, until you get rid of it by using the Reset Action in the Vernier block, or by manually deleting it.

To get rid of the Vernier Sensor.cal file, do one of the following:

• In MINDSTORMS, click the NXT Window button (upper-left) in the NXT Controller. Click the Memory tab and then "Other" from the NXT Memory Usage list. Choose the file Vernier Sensor.cal and delete it.
• Add a Vernier Sensor block at the start of your program and set its Action as Reset.

You may be wondering why we have these Vernier Sensor.cal files. The reason is that they provide a way to zero a sensor, or in the case of a pH sensor, to calibrate a sensor. The assumption is that only advanced users will use the Zero/Calibrate action of the Vernier Sensor Block, and that they will remember to remove it when it has served its purpose.

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