Xylem Expert 7060_7070_Modbus User Manual
Page 14
Communication protocol Serie30
Page 20/37
5.2.4 Scaling the analogue output
The analogue output on the Series 30 pressure transmitters can be programmed via the interface. As the two routes sensor-
signal
Æ
digital transformation and digital value
Æ
analogue signal are calibrated independently at the factory, the analogue
output can be set to different pressures or pressure units without requiring recalibration. For this purpose, KELLER offers the
free READ30 software, which provides a convenient means of carrying out this scaling with a PC.
To programme the scaling of the analogue output yourself, proceed as follows:
Function 100 enables you to ascertain whether the device possesses an analogue output. The coefficients required for
calculation can be read out via function 30. A new scaling can be programmed via function 31.
For devices of Class.Group = 5.1 the new scaling must be updated via function 95 CMD = 4.
In the case of devices of Class.Group = 5.20 the analogue output is updated automatically.
Read-out of pressure range for the analogue output:
The following coefficients(K[no.]) must be read out via function 30 in order to calculate the lower and upper limit of the analogue
output:
A = (K[92] – K[68]) / K[69]
B = (K[93] – K[68]) / K[69]
Setting a new pressure range for the analogue output:
K[68] and K[69] must be calculated and written into the device via function 31:
K[68] = K[92] - ((K[93] – K[92]) / (B – A)) * A
K[69] = (K[93] – K[92]) / (B – A)
Whereby:
K[x]: Coefficient with the corresponding number [x] Æ see function 30
A:
Pressure in bar at which the signal K[94] is to be output
B:
Pressure in bar at which the signal K[95] is to be output
Other pressure units are to be converted into bar.
5.3
Function 31: Write coefficient
Request:
DevAddr 31
Nr.
B3
B2
B1
B0
CRC16_H CRC16_L
Response:
DevAddr 31
0
CRC16_H CRC16_L
Exception errors:
2
If no. is not 53, 64 .. 73, 78, 79 or 100 .. 111
3
If message length is incorrect
32
If device has not yet been initialised
Note:
Information on scaling of the channels: See functions 73 and 95. Information on which channels are active: See function 100.
Device of Class.Group = 5.1: DAC scaling only, no. 68 and 69 can be specified.
Device of Class.Group = 5.20: No. 64 .. 71 can be specified.
MJK do