HP WaterSkis E1412A Set Autozero to Once or OFF Turn Autorange, Decrease Aperture Time or NPLCs

Set Autozero to ONCE or OFF

Turn Autorange

OFF

Autozero causes the A/D to alternately measure its internal zero and the external signal. Autozero improves reading accuracy; however, it reduces reading speed by ½.

CAL:ZERO:AUTO	ON ----The zero will be measured before each
	measurement.
CAL:ZERO:AUTO	OFF ----No new zero readings will be made.
CAL:ZERO:AUTO	ONCE----Does one Autozero operation when the
	command is received and also sets the mode
	to autozero OFF.

The zero may vary over time, especially as the room temperature varies. Noticeable changes can be expected over many minutes or hours. However, over a few seconds the changes should be very small.

Turning autorange OFF makes the HP E1312A and HP E1412A take all measurements on a fixed range which results in fast and predictable measurement times.

Autorange is turned OFF when a numeric value or MINMAX is specified for the <range> parameter of the CONFigure, MEASure, [SENSe:]RESistance:RANGe, [SENSe:]VOLTage:RANGe, or [SENSe:]VOLTage:AC:RANGe command. Autorange is directly controlled by the [SENSe:]VOLTage:RANGe:AUTO ONOFF, [SENSe:]VOLTage:AC:RANGe:AUTO ONOFF, or [SENSe:]RESistance:RANGe:AUTO ONOFF command.

You can query the HP E1312A or HP E1412A autorange status for a particular function by the following commands:

[SENSe:]CURRent[:DC]:RANGe:AUTO?

[SENSe:]CURRent:AC:RANGe:AUTO?

[SENSe:]FREQuency:VOLTage:RANGe:AUTO?

[SENSe:]FRESistance:RANGe:AUTO?

[SENSe:]PERiod:VOLTage:RANGe:AUTO?

[SENSe:]RESistance:RANGe:AUTO?

[SENSe:]VOLTage[:DC]:RANGe:AUTO?

[SENSe:]VOLTage:AC:RANGe:AUTO?

[SENSe:]RESistance:RANGe:AUTO?

Decrease Aperture Time or NPLCs

The aperture time or NPLCs (number of power line cycles) is the amount of time that the input signal is integrated. The smaller the aperture time or NPLCs, the faster the readings are taken.

A disadvantage to faster aperture times or smaller NPLC settings is increased noise will be present in the measured values. The most common source of noise is from AC power sources.

The magnitude of noise from AC power sources in most cases is many millivolts. If the signal being measured is large enough, then the noise may not be significant. However, noise becomes a factor if the signal being measured is in the microvolt range.

Appendix C Measurement Speed and Accuracy Trade-offs 197