John and others following this,
The AZ(auto zero function) and Manual/Auto? functions are two different animals.
The AZ function shorts the input to the DC conditioning amplifier, U101, before each measurement of the customer's input to determine any residual offset of the input due to thermal drift and subtract that offset value from the input being measured.? ?So in principle if the input offsets drift over changes of time and temperature with a shorted input, the display will continue to read ZERO.?
Internal switches inside the input hybrid U102 are called? ? ?MZ -measure ZERO? and? MC -measure CUSTOMER (input)
With Auto Zero ON,? two readings are made for each measurement registered on the display:
[1]:? measure the offsets:? ?(MZ switch ON,? ?MC-measure customer switch OFF)? ? ? ? ? ? ? ?
[2]:? ?measure the customer input:? ?(MC switch ON, MZ switch OFF)? ? ? ? ? ??
[3}:? subtract [1]? from [2] and display the value
If the AZ function is turned OFF, the input remains static with the input constantly applied to the input of U101.? The reading rate in this condition is effectively doubled because the MZ and MC switches are no longer being toggled and all measurements are a measure customer with no new offsets being measured.? The ZERO from the last time AZ was active is subtracted from the customer input until AZ is turned on again.? So if you have AZ turned OFF, it is a good practice to turn it on periodically to get a new ZERO reading if the environment is unstable that may cause the input offsets to drift.
Manual range and Auto ranging is independent of the AZ function.? ?The meter can stay fixed on a given range or auto range with or without the AZ function turned ON.
Hope this helps you,
George? ? ? ? March 18, 2019? ? 11:02 am
