MEASure[:VOLTage]:AC?
Syntax
MEASure[:VOLTage]:AC? [{<range>|AUTO|MIN|MAX|DEF} [,{<resolution>|MIN|MAX|DEF}] , ] [(@<ch_list>)]
Description
First, this command resets all measurement parameters on the specified channels to their default values. Then, configures the channels for ac voltage measurements and immediately sweeps through the specified channels one time (independent of the present scan list). The results are sent directly to reading memory and the instrument's output buffer. If you omit the optional <ch_list> parameter, this command applies to the internal DMM, independent of any channels.
Used With:
34921A through 34925A Multiplexer Modules
Parameters
|
Name |
Type |
Range of Values |
Default Value |
|
<range> |
Numeric |
Expected value in volts (ranges shown below). 100 mV (MIN) |
AUTO (autorange) |
|
<resolution> |
Numeric |
Desired resolution in volts. |
Fixed at 6 |
|
<ch_list> |
Numeric |
One or more channels in the form (@sccc). |
If <ch_list> is omitted, this command applies to the internal DMM. |
Remarks
By default, the instrument scans the list of channels in ascending order from slot 1 through slot 8 (channels are reordered as needed). If your application requires non-ordered scanning of the channels in the present scan list, you can use the ROUTe:SCAN:ORDered command to enable the non-sequential scanning mode. In either mode, channels which are not in the scan list are skipped during the scan.
For sequential scanning (default, ROUT:SCAN:ORDERED ON), the specified channels are reordered as needed and duplicate channels are eliminated. For example, (@2001,1003,1001,1003) will be interpreted as (@1001,1003,2001).
For non-sequential scanning (ROUT:SCAN:ORDERED OFF), the channels remain in the order presented in the scan list (see exception below). Multiple occurrences of the same channel are allowed. For example, (@2001,2001,2001) and (@3010,1003,1001,1005) are valid and the channels will be scanned in the order presented.
When you specify a range of channels in the scan list, the channels are always sorted in ascending order, regardless of the ROUTe:SCAN:ORDered setting. Therefore, (@1009:1001) will always be interpreted as 1001, 1002, 1003, etc.
The Analog Bus relays are automatically opened and closed as required during the scan to connect to the internal DMM for the measurement. For example, all 2-wire measurements use the ABus1 (MEAS) relays; for 4-wire measurements, the ABus2 (SENS) relays are used in addition to the ABus1 relays.
If you specify a <ch_list> with the MEASure? command, the instrument performs a "temporary" scan of the specified channels (independent of the present scan list as set by the ROUTe:SCAN command). The following rules apply while the temporary scan is running (these rules supersede the rules for the pre-existing scan list, but that scan list is not modified).
When the temporary scan is initiated, the instrument will open all channels in banks that contain one or more channels in the <ch_list>.
In order to guarantee that no signals are connected to the Analog Buses prior to the temporary scan, the instrument will open all ABus1 relays (applies to all banks in all slots). In banks that contain channels in the <ch_list>, the instrument will also open all ABus2 relays (regardless of whether 4-wire measurements are involved). If no channels configured for 4-wire measurements are included in the <ch_list>, the state of the ABus2 relays in the non-scanned banks is not altered.
The state of the ABus3 and ABus4 relays is not altered and these relays remain available for use during the scan. However, be sure to use CAUTION when closing these relays on banks involved in the temporary scan. While the scan is running, any signals present on ABus3 and/or ABus4 will be joined with the scanned measurement on ABus1 and ABus2. If you have any doubt regarding the state of the ABus3 and ABus4 relays, it is recommended that you send a ROUTe:OPEN:ABUS ALL command prior to scanning operations.
While the temporary scan is running, the instrument prevents use of all channels in banks that contain one or more channels in the specified <ch_list> (these channels are dedicated to the temporary scan). In addition, the instrument prevents use of all ABus1 and ABus2 relays on banks containing channels in the <ch_list>. If one or more channels configured for 4-wire measurements are included in the <ch_list>, then the rules for ABus2 relay operations are extended to the non-scanned banks as well.
At the end of the temporary scan, the last channel that was scanned will be opened (as well as any Analog Bus relays used during the scan). Any channels that were opened during the scan will remain open at the completion of the scan.
If you omit the optional <ch_list> parameter, the configuration applies to the internal DMM, independent of any channels or a scan list (any existing scan list is not redefined). An error is generated if the internal DMM is not installed or is disabled.
When you specify a range of channels with this command, any channels that are invalid will be ignored (no error will be generated) but the first and last channel in the range must be valid for the selected function. The Analog Bus relays (numbered s911, s912, s913, etc.) on the multiplexer and matrix modules are ignored if they are included in a range of channels. An error will be generated if an Analog Bus relay is specified as the first or last channel in a range of channels.
You can allow the instrument to automatically select the measurement range using autoranging or you can select a fixed range using manual ranging. Autoranging is convenient because the instrument decides which range to use for each measurement based on the input signal. For fastest scanning operation, use manual ranging on each measurement (some additional time is required for autoranging since the instrument has to make a range selection).
If you select autoranging (by specifying "AUTO" or "DEF"), an error will be generated if you specify a discrete value for the <resolution> parameter. When autoranging is combined with a discrete resolution, the instrument cannot accurately resolve the integration time (especially if the input signal is continuously changing). If your application requires autoranging, be sure to specify "DEF" for the <resolution> parameter or omit the parameter from the command.
-
Autorange thresholds:
Down range at:
<10% of range
Up range at:
>120% of range
If the input signal is greater than can be measured on the selected range (manual ranging), the instrument gives an overload indication: "±OVLD" from the front panel or "±9.9E+37" from the remote interface.
For ac measurements, the resolution is fixed at 6
½ digits. The only way to control the reading rate for ac measurements is by changing the channel delay or by setting the ac filter to the highest frequency limit. The <resolution> parameter only affects the number of digits shown on the front panel.The default trigger delays for ac measurements (see TRIGger:DELay:AUTO and ROUTe:CHANnel:DELay:AUTO commands) do not account for worst case settling delays that can occur when measuring ac signals with large dc offsets. Significant measurement errors may result. Use the TRIGger:DELay command (for stand-alone DMM measurements) or ROUTe:CHANnel:DELay command (for scanned measurements) to allow adequate settling time before the measurement.
The 34923A, 34924A, and 34933A modules use non-latching reed relays. Due to power dissipation issues, there is a limit to the number of relays that can be closed at a time on these modules (you cannot close all channels simultaneously). See the ROUTe:CLOSe command for details.
The Safety Interlock feature prevents connections to the Analog Buses if no terminal block or properly-wired cable is connected to the module. An error will be generated if scanning is performed on banks without a terminal block or properly-wired cable. See the SYSTem:ABUS:INTerlock:SIMulate command to temporarily disable errors generated by the Safety Interlock feature.
The *RST command will clear the scan list and set all measurement parameters to their factory settings. The Instrument Preset (SYSTem:PRESet command) will not clear the scan list; however, this command will clear reading memory and all stored statistical data.
Return Format
The command returns one reading for each channel specified (multiple responses are separated by commas). If you omit the <ch_list> parameter, the command applies to the internal DMM and a single reading is returned. The output from this command is not affected by the settings of the FORMat:READing commands.
Examples
The following command configures
the instrument for ac voltage measurements, triggers the internal DMM
to scan one channel (channel 4 in slot 3), and then transfers the reading
to reading memory and the instrument's output buffer. The default range
(autorange) and resolution (fixed at 6
MEAS:VOLT:AC? (@3004)
Typical Response: +1.86850000E-03
The following command configures the instrument for ac voltage measurements, triggers the internal DMM to scan two channels (channels 3 and 8 in slot 1), and then transfers the reading to reading memory and the instrument's output buffer. The 1 V range is selected.
MEAS:VOLT:AC? 1,(@1003,1008)
Typical Response: +4.27150000E-03,+1.32130000E-03
The following command configures the internal DMM for an ac voltage measurement (no <ch_list> is specified), triggers the internal DMM, and then transfers the reading to reading memory and the instrument's output buffer. The default range and resolution are used for the measurement.
MEAS:VOLT:AC? !Applies to the internal DMM
Typical Response: +1.26360000E-02