RS-485

The MRL-6.1 is equipped with a RS-485 port to acquire sensor measurements.

Principles

The example below illustrates the acquisition of measurement values from three digital sensors with the same measurement duration.

Figure 17 Principal of data acquisition by RS-485

In polling mode the MRL-6.1 activates the RS-485 interface at the beginning of each measurement interval and sends a measurement command to the addressed sensors. If this command is not confirmed by a sensor it is re-sent a 2nd or 3rd time. As soon as all measurements have been completed and the requested results have been received within Timeout, the RS-485 interface is switched off automatically and remains idle until the next measurement interval.

NOTE  

If multiple sensors are connected to a MRL-6.1, the measurement values must be polled in sequence to avoid data transmission conflicts. To do so, set Polling delay to a few seconds. As a result, the MRL-6.1 waits for the duration of Polling delay before it requests the data of the next sensor.

The Polling delay and the measurement duration of every sensor must match the duration of Timeout. If Timeout is too short, the MRL-6.1 may not receive all measurement values.

For example, sensor one has a measurement duration of 10 seconds, sensor two has a measurement duration of 30 seconds and Polling delay is 2 seconds, Timeout should be at least 10 + 2 + 30 = 42 seconds, plus a few seconds for processing delays.