10 CHANNELS, Coupling & Probes

Size: px

Start display at page:

Download "10 CHANNELS, Coupling & Probes"

Sibyl Wright
6 years ago
Views:

10 CHANNELS, Coupling & Probes Channel Controls These controls enable selection of displayed traces and the adjustment of vertical sensitivity and offset. See Chapter 5 for DRIVE ANALYSIS.

1 10 CHANNELS, Coupling & Probes Channel Controls These controls enable selection of displayed traces and the adjustment of vertical sensitivity and offset. See Chapter 5 for DRIVE ANALYSIS. CHANNEL SELECT If the channel trace is not already displayed, pressing these buttons displays the corres-ponding channel trace. If the channel trace is displayed, pressing them will select the corresponding channel trace. The selected channel number is highlighted in the Acquisition Summary field (see chapter 4), and all the vertical controls are attributed to this selected channel. If the channel trace has already been selected, these buttons will switch off the corresponding channel trace. This knob vertically positions the active channel. This selects the vertical sensitivity factor either in a sequence or continuously (see VAR, below). The effect of gain changes on the acquisition offset can be chosen from the SPECIAL MODES menu. WP-DDA-UG-E Rev A ISSUED: October

2 CHANNELS, Coupling & Probes Coupling Press a channel select button to choose a coupling level that adapts the DDA s input impedance to the impedance of the device under test. It also displays menus that offer a selection of: Coupling and grounding of each input channel ECL or TTL gain, offset and coupling preset for the channel shown Bandwidth limit for all channels Probe attenuation of each input channel Coupling This is used to select the input channel s coupling. If an overload is detected, the instrument will automatically set the channel to the grounded state. The menu can then be reset to the desired coupling. V/div Offset When NORMAL is highlighted, pressing the corresponding menu button sets the offset, Volts/div, and input coupling to display ECL signals. Press the button a second time and the settings for TTL signals are given. Pressing it a third time returns the settings to those used at the last manual setup of the channel. Global BWL/BWL Use this to turn the bandwidth limit Off or to select a limit. The bandwidth can be reduced from the maximum to either 200 MHz or 25 MHz. Bandwidth limiting is useful for reducing signal and system noise or preventing high-frequency aliasing, reducing, for example, any high-frequency signals that may cause aliasing in single-shot applications. This menu appears as Global BWL if the Global BWL is activated (see Chapter 19, Special Modes ), when the limit set will apply to all channels. It appears as BWL if the Global BWL is deactivated, when a limit can be set individually for each channel ISSUED: October 2000 WP-DDA-UG-E Rev A

3 DDA Probe Atten This sets the probe attenuation factor related to the input channel (see the following section for probe details). Notes on Coupling: In the AC position, signals are coupled capacitively, thus blocking the input signal s DC component, and limiting the signal frequencies below 10 Hz. In the DC position, all signal frequency components are allowed to pass through, and 1 MW or 50 W may be chosen as the input impedance. The maximum dissipation into 50 W is 0.5 W. Whenever this is attained: 1. Inputs will automatically be grounded 2. An overload message will be displayed in the Acquisition Summary Field 3. The overload condition can be reset by removing the signal from the input and selecting, again, the 50 W input impedance from the menu 4. Grounded will be highlighted in the Coupling menu. WP-DDA-UG-E Rev A ISSUED: October

CHANNELS, Coupling & Probes Probes and Probe Calibration A LeCroy PP005 passive probe Four passive probes one for each channel are supplied with the DDA.

4 CHANNELS, Coupling & Probes Probes and Probe Calibration A LeCroy PP005 passive probe Four passive probes one for each channel are supplied with the DDA. To calibrate these, proceed as follows (see also the separate probe instruction sheet provided): 1. Turn on the DDA. 2. When using the HF-compensation ground lead, insert the lead s pins into the probe head, and connect the probe to one of the input channels/bnc connectors. 3. Attach the lead s alligator clip to the CAL BNC s ground (outer ring) and touch the tip to its inner conductor. Alternatively, when using the 11-cm ground lead, attach the supplied BNC adapter to the CAL BNC and, having connected the probe to an input channel, insert the probe tip in the adapter. The CAL signal in both cases will be a 1-kHz square wave, 1 V p p. 4. Set the channel coupling to DC 1 MW using the Coupling menu, and press the ON/OFF/SELECT button to activate the desired choice. 5. Press to set up the DDA. If overshoot or undershoot of the displayed signal occurs, the probe can be adjusted by inserting the small screwdriver, supplied with the probe package, into the trimmer on the probe s barrel and turning it to achieve the optimal square-wave contour. ProBus Probe System For other probes, LeCroy s ProBus system provides a complete measurement solution from probe tip to display. This intelligent interconnection between LeCroy s Disk Drive Analyzer and a wide range of accessories is achieved using a bus that follows Philips I 2 C protocol. ProBus offers important advantages over standard BNC 10 4 ISSUED: October 2000 WP-DDA-UG-E Rev A

5 DDA Illustrated at right: a LeCroy current probe with ProBus connection. and probe ring connections. The system ensures correct input coupling by auto-sensing the probe type, eliminating the guesswork and errors that occur when attenuation or amplification factors are set manually. ProBus also allows control of transparent gain and offset from the front panel, particularly useful for dfferential FET and current probes. It uploads Gain and offset correction factors from the ProBus EPROMS on FET probes, automatically compensating to achieve fully-calibrated measurements. Coupling This is used to select the input channel s coupling. If an overload is detected, the instrument will automatically set the channel to the grounded state. The menu can then be reset to the desired coupling. V/div Offset When NORMAL is highlighted, pressing the corresponding menu button sets the offset, Volts/div, and input coupling to display ECL signals. Press the button a second time and the settings for TTL signals are given. Pressing it a third time returns the settings to those used at the last manual setup of the channel. Global BWL/BWL Use this to turn the bandwidth limit Off or to select a limit. The bandwidth can be reduced from the maximum to either 200 MHz or 25 MHz. Bandwidth limiting is useful for reducing signal and system noise or preventing high-frequency aliasing, reducing, for example, any high-frequency signals that may cause aliasing in single-shot applications. This menu appears as Global BWL if the Global BWL is activated (see Chapter 19, Special Modes ), when the limit set will apply to all channels; as BWL if the Global BWL is deactivated, when a limit can be set individually for each channel. WP-DDA-UG-E Rev A ISSUED: October

6 CHANNELS, Coupling & Probes When a FET probe is used Probe sensed automatically appears to indicate settings. When other ProBus probes are used, this is redefined ISSUED: October 2000 WP-DDA-UG-E Rev A

7 DDA BLANK PAGE WP-DDA-UG-E Rev A ISSUED: October

CLEANING CALIBRATION INTERVAL

&DUHDQG0DLQWHQDQFH! &DUHDQG0DLQWHQDQFH CLEANING CALIBRATION INTERVAL SERVICE STRATEGY TROUBLESHOOTING A. Trace Off Scale The exterior of the probe and cable should be cleaned only using a soft cloth moistened