Run a macro based on sample ID on RTD

Question

I want to run the mail macro whenever cell B1 change. I need this to happen without manual intervention because B1 is changed due to incoming RTD(OPC) server data. As it stands, unless I manually update something in my sheet the macro does not run. rang("b1") is from RTD

Public Sub Worksheet_Change(ByVal Target As Range)
Dim sampleID As String
If Range("B1") <> sampleID Then
sampleID = Range("B1")
Call mail
End If

when I change b1 manually. it will call mail Marco but when RTD change it don't workt