Chapter 3 Features and Functions

Math Operations

Math Operations

There are five math operations available, only one of which can be enabled at a time. Each math operation performs a mathematical operation on each reading or stores data on a series of readings.

The selected math operation remains in effect until you disable it, change functions, turn off the power, or perform a remote interface reset. The math operations use one or more internal registers. You can preset the values in some of the registers, while others hold the results of the math operation.

From the front panel, you enable a math operation by pressing the appropriate key. The exception is Limit Test which you enable using the

LIMIT TEST command in the MATH MENU.

From the remote interface, the math operations and registers are controlled using commands within the CALCulate command subsystem. First, select the math operation you want to use (the default function is null):

CALCulate:FUNCtion {NULL|DB|DBM|AVERage|LIMit}

Then, enable the selected math function by turning the math state on:

CALCulate:STATe ON

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Min–Max Operation

The min-max operation stores the minimum and maximum readings during a series of measurements. The multimeter then calculates the average of all readings and records the number of readings taken since min-max was enabled.

Applies to all measurement functions, except continuity and diode.

•After you enable min-max, the first reading that the multimeter takes is stored as both the minimum and maximum value.

The minimum is replaced with any subsequent value that is less. The maximum is replaced with any subsequent value that is greater.

•The multimeter displays “MIN” or “MAX” and beeps (if the front-panel beeper is enabled) whenever a new minimum or maximum is found. It is possible that the multimeter will beep even if the displayed reading does not change; this is because the multimeter’s internal resolution may be greater than the displayed resolution. See also “Beeper Control,” on page 88.

•The minimum, maximum, average, and count are stored in volatile memory; the multimeter clears the values when min-max is turned on, when power has been off, or after a remote interface reset.

•Front-Panel Operation: After enabling min-max, you can read the stored minimum, maximum, average, and count by pressing

Shift > (Menu Recall). Turning on the menu does not disable the min-max operation; the multimeter will resume taking measurements when you turn off the menu.

1: MIN-MAX (MATH MENU)

See also “To Store Minimum and Maximum Readings,” on page 39.

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•Remote Interface Operation: You can use the following commands to make min-max measurements.

Null (Relative) Operation

When making null measurements, also called relative, each reading is the difference between a stored null value and the input signal. One possible application is in making more accurate two-wire ohms measurements by nulling the test lead resistance.

Result = reading – null value

Applies to all measurement functions, except continuity, diode, and ratio.

•The null value is adjustable and you can set it to any value between 0 and ±120% of the highest range, for the present function.

•The null value is stored in volatile memory; the value is cleared when power has been off, after a remote interface reset, or after a function change.

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dB Measurements

Each dB measurement is the difference between the input signal and a stored relative value, with both values converted to dBm.

dB = reading in dBm – relative value in dBm

Applies to dc voltage and ac voltage measurements only.

•The relative value is adjustable and you can set it to any value between 0 dBm and ±200.00 dBm.

when power has been off, after a remote interface reset, or after a function change.

•The relative value is stored in the multimeter’s dB Relative Register. There are two ways you can specify the relative value. First, you can enter a specific number into the register from the front-panel menu or from the remote interface. Any previously stored value is replaced with the new value. If you are operating the multimeter from the front panel, entering a relative value also turns on the dB function.

The second way to enter the relative value is to let the multimeter take the first reading, convert it to dBm, and store that value in the register. Changing the dBm reference resistance (see page 68) does not change the stored relative value. After you enable dB, the first reading taken will be 0 dB (if you have not changed the value stored in the register). If you entered a number into the register, as described in the paragraph above, the first reading does not overwrite the stored value.

•Front-Panel Operation: After enabling dB, you can edit the stored

relative value by pressing Shift > (Menu Recall). Any previously stored value is replaced with the new value. Turning on the menu does not disable the dB operation; the multimeter will resume taking measurements when you turn off the menu.

3: dB REL (MATH MENU)

See also “To Make dB Measurements,” on page 40.

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•Remote Interface Operation: You can use the following commands to make dB measurements. Math must be enabled before you can store a value to the Relative Register.

CALCulate:FUNCtion DB CALCulate:STATe {OFF|ON}

CALCulate:DB:REFerence {<value>|MINimum|MAXimum}

dBm Measurements

The dBm operation calculates the power delivered to a resistance referenced to 1 milliwatt.

dBm = 10 × Log10 ( reading2 / reference resistance / 1 mW )

Applies to dc voltage and ac voltage measurements only.

•You can choose from 17 different reference resistance values. The factory setting for the reference resistance is 600Ω .

The choices are: 50, 75, 93, 110, 124, 125, 135, 150, 250, 300, 500, 600, 800, 900, 1000, 1200, or 8000 ohms.

•The reference resistance is stored in non-volatile memory, and does not change when power has been off or after a remote interface reset.

•Front-Panel Operation: After enabling dBm, you can select a new

reference resistance by pressing Shift > (Menu Recall). Turning on the menu does not disable the dBm operation; the multimeter will resume taking measurements when you turn off the menu.

4: dBm REF R (MATH MENU)

See also “To Make dBm Measurements,” on page 41.

•Remote Interface Operation: You can use the following commands to make dBm measurements.

CALCulate:FUNCtion DBM

CALCulate:STATe {OFF|ON} CALCulate:DBM:REFerence {<value>|MINimum|MAXimum}

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Limit Testing

The limit test operation enables you to perform pass/fail testing to upper and lower limits that you specify.

Applies to all measurement functions, except continuity and diode tests.

•You can set the upper and lower limits to any value between 0 and

±120% of the highest range, for the present function. The upper limit selected should always be a more positive number than the lower limit. The default upper and lower limits are both “0”.

multimeter sets both limits to “0” when power has been off, after a remote interface reset, or after a function change.

•You can configure the multimeter to generate a service request (SRQ) on the first occurrence of a failed reading. See “The SCPI Status Model,” starting on page 134 for more information.

•Front-Panel Operation: The multimeter displays “OK” for each reading that is within the specified limits. It displays “HI” or “LO” for each reading that exceeds the upper or lower limit. The multimeter beeps once (if the front-panel beeper is enabled) on the first occurrence of a failed reading after a good reading. See also “Beeper Control,” on page 88.

You can also turn off limit test by selecting a different math operation from the front panel (only one math operation can be enabled at a time).

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