HP WaterSkis E1312A, WaterSkis E1412A Loading Errors ac volts, AC Measurements Below Full Scale

Loading Errors (ac volts)

In the ac voltage function, the input of the HP E1312A and HP E1412A appears as a 1MW resistance in parallel with 100pF of capacitance. The cabling that you use to connect signals to the multimeter will also add additional capacitance and loading.

For low frequencies where (f × Rs) ≤ 15(106)Ω ∙ Hz: :

-100 ´ Rs
Error (%) = R----s---+-----1M--------Ω--
For any frequency:
	1			1MΩ
Error (%) = 100 x [ ---------------------------------------------------------------		×	(1MΩ)R	( 1M--------------------Ω+Rs)-1]
1 + (2p f C	in		------------------------1MΩ+R	s)2
				s
Rs = source resistance

f= input frequency

Cin = input capacitance (100pF) plus cable capacitance

AC Measurements Below Full Scale

You can make the most accurate ac measurements when the multimeter is at full scale of the selected range. Autoranging occurs at £10% and ³120% of full scale. This enables you to measure some inputs at full scale on one range and 10% of full scale on the next higher range (e.g., 10V on the 10V range or 10V on the 100V range). The accuracy will be significantly different for these two cases. For highest accuracy, you should specify the range to assure the lowest range possible for the measurement (this turns autorange off).

Function and Range

Change Internal

Offset Correction

Temperature Coefficient Errors

The HP E1312A and HP E1412A uses an ac measurement technique that measures and removes internal offset voltages when you select a different function or range. The next two sections discuss two ways these offset errors can be generated and how the multimeter deals with them.

If you leave the multimeter in the same range for an extended period of time, and the ambient temperature changes significantly (or if the multimeter is not fully warmed up), the internal offsets may change. This temperature coefficient is typically 0.002% of range per °C and is automatically removed when you change functions or ranges.

Overload Errors When you specify a new range in an overload condition, the internal offset measurement may be degraded for the selected range. Typically, an additional 0.01% of range error may be introduced. This additional error is automatically removed when you remove the overload condition and change function or range; the error remains if the function or range is not changed.

34 HP E1312A/E1412A Multimeter Application Information Chapter 2