Fluke 2620A, 2625A user manual

Operating the Instrument from the Front Panel	3
Channel Configuration

be changed at any point is brightly lit (solid for digits, flashing for other annunciators); all other elements are dimly lit at this time. Table 3-9 presents a full description of the Mx+B configuration sequence.

If you press Cwhile setting the "M" value (anytime prior to showing the "B" value), no changes entered thus far are stored. If you press Cwhile setting the "B" value, changes to M are stored and changes to "B" are discarded. In either case, the instrument returns to Inactive Mode.

The final Epress shown in Table 3-9 stores all changes and returns the instrument to Inactive Mode.

Note

Once Mx+B scaling values are defined for a channel, the instrument uses the range chosen for the B value as the display range for the resulting scaled value. If the result is larger than the display range chosen, an overload ("OL") is displayed.

For example, you could monitor the output of a high-pressure pump by using Mx+B scaling to convert the millivolt output of a pressure transducer to PSI. Such a transducer might output 0 to 30 mV, corresponding to pressure of 0 to 5000 PSI. The scaling values to convert the transducer millivolts to PSI would be M = 166.67 PSI/V and B = 0 PSI, calculated as follows:

Max Display Value	Min Display Value	5000
M =	=	= 166.67
Max Transducer Output	Min Transducer Output	30

B = Min Display Value - (M * Min Transducer Output) = 0 - 166.67 * 0 = 0

When a channel that has had scaling values entered is scanned or monitored, the resulting scaled value is displayed without the underlying function annunciation. The decimal point location and scale factor for the result is fixed by the "B" value entered. If the scaled value is too small to be represented in 5 digits given this scaling, zero is displayed. If the scaled value is too large, "OL" (overload) is displayed (even if the underlying measurement was on scale.) "OL" is also displayed if the measurement is in overload.

If scanning or monitoring a scaled channel gives unexpected results (like zero or overload), make the following checks:

1.Verify that the values and scale factors of "M" and "B" are set as intended.

2.Verify that the desired values are the correct values: calculate the result for a few measured values using the entered "M" and "B".

3.Temporarily set "M" to 1 and "B" to 0; verify that the measurements are returning values in the expected range. Unexpected measurements could result from a wiring error or the wrong range/function being selected.

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