Item Scaling

Overview

All protocol modules support the scaling of item values. This allows client applications to view or change data based on calculated formula instead of raw device data. Any item can be scaled, with the exception of Boolean (bit) and String items. After scaling the original item data type will be changed to Double.

To apply scaling to an item, use the following syntax as the OPC item name:

Linear Scaling

ItemName{SL:LR:HR:LE:HE}
LowRaw, HighRaw, LowEGU, HighEGU in "{SL:LR:HR:LE:HE}"

Validate lows are lower than highs.

• ItemName is any valid item.
• SL is the linear scale identifier and must appear after the open bracket.
• LR is the low raw value.
• HR is the high raw value. 
• LE is the low engineering value. 
• HE is the high engineering value.

Below is SL formula used to calculate scaled data after reading from device:

Scaled = (Raw-LoRaw)/(HiRaw-LoRaw)*(HiEGU-LoEGU)+LoEGU

Example: Device1.40001{SL:0:4095:0:100}

If device returns raw value 1000 the scaled value should be:

Scaled = (1000 - 0)/(4095 - 0)*(100 - 0) + 0 = 24.42

This sample shows how the raw data of 1000 was calculated with SL formula to generate the result of 24.42.

Below is SL formula used to calculate raw data before sending to device:

Raw = (Scaled-LoEGU)/(HiEGU-LoEGU)*(HiRaw-LoRaw)+LoRaw

Example: Device1.40001{SL:0:4095:0:100}

If a scaled value of 60 was written to the device then the actual data written to the device will be:

Raw = (60 - 0)/(100 - 0)*(4095 - 0) + 0 = 2457

The above sample shows how the scaled value of 60 is written to the device as actual raw value of 2457.

Square root Scaling

ItemName{SQ:LR:HR:LE:HE}
LowRaw, HighRaw, LowEGU, HighEGU in "{SQ:LR:HR:LE:HE}"

Validate lows are lower than highs.

• ItemName is any valid item.
• SQ is the square root scale identifier and must appear after the open bracket.
• LR is the low raw value.
• HR is the high raw value.
• LE is the low engineering value.
• HE is the high engineering value.

Below is the SQ formula used to calculate scaled data after reading from device:

Scaled = SQRT((Raw-LoRaw)/(HiRaw-LoRaw))*(HiEGU-LoEGU)+LoEGU

Example: Device1.40002{SQ:0:4095:0:100}

If device returns raw value 1000 the scaled value should be:

Scaled = SQRT((1000 - 0)/(4095 - 0))*(100 - 0) + 0 = 49.42

This sample shows how the raw data of 1000 was calculated with the SQ formula to generate the result of 49.42.

Below is the SQ formula used to calculate raw data before sending to device:

Raw = ((Scaled-LoEGU)/(HiEGU–LoEGU))^2*(HiRaw-LoRaw)+LoRaw

Example: Device1.40002{SQ:0:4095:0:100}

If a scaled value of 60 was written to the device then the actual data written to the device will be:

Raw = ((60 - 0)/(100 - 0))^2*(4095 - 0) + 0 = 1474.2

Above sample shows how the scaled data of 60 being written to device as actual raw value of 1474.2.

Gain/Offset Scaling

ItemName{SG:Gain:Offset}
Gain, Offset in "{SG:Gain:Offset}"

Validate Gain is not zero.

• ItemName is any valid item.
• SG is the gain/offset scale identifier and must appear after the open bracket. 
• Gain is a multiplier. 
• Offset is an addition.

Below is the SG formula used to calculate scaled data after reading from device:

Scaled = Raw * gain + offset

Example: Device1.40003{SG:2.5:1}

If the device returns raw value of 1000 the scaled value should be:

Scaled = 1000 * 2.5 + 1 = 2501

This sample shows how the raw data of 1000 was calculated with the SG formula to generate the result of 2501.

Below is the SG formula used to calculate raw data before sending to device:

Raw = (Scaled - offset) / gain

Example: Device1.40003{SG:2.5:1}

If a scaled value of 60 was written to the device then the actual data written to the device will be:

Raw = (60 - 1)/2.5 = 24.4

The above sample shows how the scaled data of 60 was written to the device as actual raw value of 24.4.

Inverse Scaling

ItemName{SI:Inverse} or {SI}
Inverse in "{SI:Inverse}" or “{SI}”

Validate that Item raw value is not zero

• ItemName is any valid item.
• SI is the inverse scale identifier and must appear after the open bracket.
• Inverse is a divider.
• By default “{SI}” the inverse is 1 – {SI} is the same as {SI:1}.

Below is the SI formula used to calculate scaled data after reading from device:

Scaled = Inverse/Raw

Example: Device1.40003{SI:2}

If the device returns a raw value of 1000 the scaled value should be:

Scaled = 2/1000 = 0.002

This sample shows how the raw data of 1000 was calculated with the SI formula to generate the result of 0.002.

Below is the SI formula used to calculate raw data before sending to device:

Raw = (1/Scaled) * Inverse

Example: Device1.40003{SI:2}

If a scaled value of 0.5 was written to the device then the actual data written to the device will be:

Raw = (1/0.5) * 2 = 4

The above sample shows how the scaled data of 0.5 was written to the device as an actual raw value of 4.