Question

Hi 

I am using FMC130 device. The questions are:

1. Why analog reading for AIN2 without any input is 262mV? and 

2. after testing with different voltage inputs the analog average readings for AIN2 is 183mV?
 

Teltonika (Output)	Multimeter (Input)	Voltage Offset
1529	1357	172
1514	1327	187
1412	1236	176
1180	1001	179
948	762	186
738	549	189
729	539	190
655	471	184
609	417	192
581	403	178
568	388	180
	Average	183

Answer 1

Hello.

FMC130 has an additional error on Analog input on range 12V and on range 30V:

https://wiki.teltonika-gps.com/view/FMC130_General_description#Electrical_characteristics

Input resistance on AIN is 150 kOhms, while input resistance of typical multimeter is about 10MOhms, therefore readings may be different.

Your method is very good. Having measured additional error you can correct voltage readings on your server side.

Regards

Comments

1. How can we correct the voltage readings on our server-side? and

2. the readings from the multimeter and AIN is different because of the resistance. but without connection, it still has offset, and the offset is not consistent. our objective is to understand how do we get a correct one if there is no fixed offset that we can use to correlate?

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How can we correct the voltage readings on our server-side? - subtract 183mV from the voltage reading or if more accuracy is needed prepare offset table (as you already did) based on FM tracker readings and certified multimeter readings and use calculated offset for each range.

The case when AIN is not connected schould not be considered, voltage schould be read from voltage source, positive wire of measured voltage source schould be connected to AIN and negative to device GND.