Choosing the correct output type in wind sensor module

Thread Starter

pushparaj

Joined Oct 18, 2019
2
Hi community,

I am ordering a wind speed sensor from china. (https://www.aliexpress.com/item/819556495.html)
It has 6 output types.
1) pulse output
2) 4-20ma 3 cable
3) 0-10V 4 Cable
4) 0-2V 3 cable
5) 0-5V output
6) RS485 output

I need help in deciding which output format should i choose. They have provided speed calculation formula for pulse and 0-10volt output types only as shown below:

Pulse output type calculation:

Winds = the number of pulses within a unit time X factor;

The formula: a unit time refers 1S;

Model suffix 12CM, the coefficient is 0.1 (1m / s = 10 pulses)

______________________________________________________________________________

0-10V type calculation:

about the 0-10V .you must use DC24V power supply. red : power + ; black : power - . blue : 0-10V output
1v voltage =3m/s wind speed 2V voltage :6m/s wind speed 3V voltage =9m/s wind speed the max is 30m/s wind speed




Among these output types, is there something like one output type is better than other in terms of connection, accuracy etc ?
Do i need any additional driver/hat to decode these outputs in PI or I can connect directly like the RS485 output ?
 
Last edited by a moderator:

jpanhalt

Joined Jan 18, 2008
7,893
Welcome to AAC

What are you planning to do with the output? If you will simply be running an analog meter (voltmeter or ammeter), then options 2-5 would be best suited. If digital, option 6 is serial communication and option 1 is a type of digital where you need to do counting.

Do you plan on using an MCU? If so, does it have hardware serial communication peripherals? If hardware RS485 is supported, then that might be the way to go. If not, then counting is quite easy to do.
 

Thread Starter

pushparaj

Joined Oct 18, 2019
2
Option 6 seems good choice for me. I will have to send the data to online database. I am using raspberry PI. It supports RS485 communication. My new challenge is that I will have 3 modules which will communicate through RS485. Two wind sensors (speed and direction) and one SIM900 GSM module for sending data to online server. So, can raspberry pi support multiple RS485 connection ?
 

Picbuster

Joined Dec 2, 2013
982
Yes use 1/2 duplex and build a protocol. assuming that your sensor is able to handle a rs485 address.

Picbuster
 

Sensacell

Joined Jun 19, 2012
2,447
Note that RS-485 can be tricky on a raspberry pi due to problems with transmit/receive switchover timing.

For RS-485, one needs to switch between TX and RX mode in sync with the transmitted data, the R-pi multi-tasking OS causes latencies that make this tricky- unless you get a board that has dedicated TX-RX switching hardware to fix this.

I just dealt with this- got it working with a separate PIC chip to handle the switching, now it works flawlessly.
 
RS485 is daisy-chain master/slave bus structure. 30 some devices can be on the same "bus". The "bus" can be long. So, one port handles multiple-devices, It requires terminating resistors on both ends. It's inherently half duplex.

It can be very tricky to get to work. Some of that difficulty has been the nomenclature. I know it was difficult to get my first RS485 system to work.

You generally can convert RS485 to Ethernet and use virtual COM ports.

When using some RS232 to RS485 converters, you generally have to pause long enough to switch duplex.
 

Picbuster

Joined Dec 2, 2013
982
Note that RS-485 can be tricky on a raspberry pi due to problems with transmit/receive switchover timing.

For RS-485, one needs to switch between TX and RX mode in sync with the transmitted data, the R-pi multi-tasking OS causes latencies that make this tricky- unless you get a board that has dedicated TX-RX switching hardware to fix this.

I just dealt with this- got it working with a separate PIC chip to handle the switching, now it works flawlessly.
This true when using sync data however most of the 1/2 duplex is async.
What I normally do: all units are in receive mode master polls a device and goes in listen mode.
Device waits till line is free device answers.
When no answer lower poll interval for that device and put on the unreachable list.

No need to sync used pic int 8051 dec/ibm main frames to implement above no problems ( 120 nodes over 1000 meter)

Picbuster
 
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