16
469 MOTOR MANAGEMENT RELAY – COMMUNICATIONS GUIDE
MODBUS MEMORY MAP
COMMUNICATIONS GUIDE
To access the captured waveforms, select the waveform of interest by writing its trace
memory channel (see following table) to the Trace Memory Channel Selector (address
30F1h). Then read the trace memory data from address 3100h to 3700h. There are 720
samples per second when the nominal system frequency (modbus address 11C0) has been
set to 60 Hz or set to Variable. There are 600 samples per second when the nominal system
frequency has been set to 50 Hz. Sample rate may vary within 5% when 469 is tracking the
frequency of the input voltage. The actual sample rate for a trace is 12 x Trace Memory
Sampling Frequency, modbus address 30F9. The values read are in actual amperes or
volts.
Address 30F8h shows the number of traces taken. To access the latest use the value at
address 30F0h. To access more than 1 trace, reduce this value to access the older traces.
INTERNAL UNITS SCALE
SR 469 presents modbus values for trace data in internal units. The scale of internal units
for currents is 1 x CT = 500. The scale of internal units for voltage is 1 x VT = 2500.
Let SF
current
represent scale factor for phase current or ground current.
Let SF
voltage
represent scale factor for phase voltage.
SF
current
= (CT primary )/ (500 )
SF
voltage
= (120 V )* (VT ratio) / (2500 )
To calculate a value in units of Ampere from a waveform trace sample for Current:
Phase current [ Ampere ] = (trace sample value) * SF
current
To calculate a value in units of Volt from a waveform trace sample for Voltage:
Phase voltage [ Volt ] = (trace sample value) * SF
voltage
Table 2:
Modbus registers related to trace value scale factor
TRACE MEMORY
CHANNEL
WAVEFORM
0
Phase A current
1
Phase B current
2
Phase C current
3
Differential phase A current
4
Differential phase B current
5
Differential phase C current
6
Ground current
7
Phase A voltage
8
Phase B voltage
9
Phase C voltage
10
Relay output states
Setpoint
Description
Units of measure
1180
CT primary
Current [Ampere]
1182
Ground CT Type
Current [Ampere]
1183
Ground CT primary
Current [Ampere]
