Rearranging Of Register Value Ranges; Time Of Update - ABB Relion 620 Series Protocol Manual

1MRS757645 B
3.4.5.5
3.4.5.6
620 series
Communication Protocol Manual

Rearranging of register value ranges

The pre-defined original Modbus register does not always fit inside the whole value
range of the source value.
Example
A counter in the motor protection IED shows the running hours of the motor. The
original system counter value has a range of 0...999999 hours. For Modbus, a 16-bit
unsigned register is defined for this value. The default scale factor for this modbus
register is defined as x1.
The value range for the 16-bit register is only 0...65535. This means that when the
original counter reaches 65535 hours (about seven and half years), the Modbus value
saturates (remains locked) at 65535.
There are several ways to overcome this problem.
• It is always possible to assign the Modbus register value to a 32-bit user-definable
register. Even when the original register saturates at 65535, the user-definable
register continues calculating upwards from this value.
• Rescaling can also be applied on measurands and Modbus counter (integer)
values. The original Modbus value can be edited to show full hours, tens of hours
or days.
• If the source hour value is divided by 10, the Modbus value shows tens of
hours. This accuracy might be sufficient in many cases. Maximum Modbus
register value 65535 would then actually mean 655350 hours, or
approximately 75 years. Here the scale factor for Modbus registers is given
as a multiplicand. Division by 10 is thus same as multiplying it by 0.1
• If the source hour value is divided by 24, the Modbus value shows the
number of days. Division by 24 is same as multiplying by 0.04167.

Time of update

Some Modbus values may have a time structure attached to their values in the Modbus
memory map. This is often the case with demand measurement values. The time
structure shows the time when the value was last updated.
Vendor-specific implementation
Section 3
29