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Nicholas Vinen reviews Rohde & Schwarz new RTH1004 4-channel portable ’scope Scope Rider This 2/4-channel portable/desktop digital oscilloscope is one of the most generally useful test instruments that we have come across. It has four totally isolated input channels, each rated for 1000V (Cat III) or 600V (Cat IV) with the supplied probes, up to 300V offset between each channel, a bandwidth of up to 500MHz, optional 8-channel logic analyser and multimeter mode. A s you would expect, as new oscilloscope models are released, they tend to have more and better features than the last generation – not just more bandwidth, faster sampling and so on but also touch-screen interfaces, more mathematical display modes, more modes for measurement, analysis, triggering and so on. But sometimes it’s the seemingly simple features which come in most handy in day-to-day usage. The first feature that caught our attention on the R&S Scope Rider is the four fully isolated inputs. You would expect the inputs in a portable scope to be isolated from the power supply but these are also isolated from each other. To get the same facility in a desktop you need differential probes; a set of four such probes with the bandwidth of this unit would probably set you back more than the cost of this scope! Why is this such a big deal? Well, there are a number of situations where you might need to examine signals which do not have a common ground. For example, circuits with multiple ground domains or multiple reference voltages, signals with a DC offset where the offset may also contain AC components, measuring the voltage across high-side shunt resistors or emitter resistors, floating Mosfet gate drive signals, 80  Silicon Chip mains devices which switch the Neutral conductor and so on. Spend any significant amount of time with a scope and you will run into one or more of these situations. The usual solution is to break out a differential probe but this has many drawbacks: you need to own one or more differential probes each of will have their own power supplies, but limited bandwidth, limited operating voltage ranges but they add their own noise to the signal, complicate the wiring. etc, etc. Basically, having to use differential probes generally makes measurement more tricky and less reliable (sometimes downright misleading). There’s also the fact that when you’re dealing with low-level or high-frequency signals, you really need to connect the ground clips for each probe into the circuit and when doing so there’s always the possibility you will clip onto to the wrong part of the circuit and short it out via the scope’s Earth wiring, possibly damaging the device under test and maybe the scope too! With fully isolated inputs, all these problems are eliminated. You simply connect each probe to the signal you’re interested in and the “Earth” clip to its reference voltage (ground or whatever). There’s no possibility of shorting anything out, no loss of bandwidth – you just make the connections and siliconchip.com.au The R&S Scope Rider has an 8-inch touchscreen, jog wheel and large buttons for control. The Ch1-4 buttons illuminate when a given channel is active while the timebase control buttons are immediately above and vertical controls below. ground which is significantly below the Mosfet’s source voltage, hence the trace goes negative. Of course, you could monitor all these voltages using a traditional 4-channel scope with single-ended inputs but the voltage measurements for all but the bottom-most cell would require some interpretation and similarly, most Mosfet gate voltages would not be relative to their sources and so it may not be obvious whether they are on or off. The situation would be even more difficult if the voltages were not so steady, as is the case in some circuits. To give another example, look at Scope2. It shows the piezo driver waveforms of the Hotel Safe Alarm described elsewhere in this issue. The yellow and green traces show the complementary drive signals coming from the PIC16F88 microcontroller and these have the same common earth point. The red trace shows the summed drive signal across the transducer which is effectively being driven in bridge mode. To get the same signal display in a typical desktop scope you would have to resort to a differential probe or the MATH mode (showing the difference between the complementary signals). On this portable scope, it’s easy. Finally, Scope3 and Scope4 show another situation where you would normally want a differential probe with a high isolation voltage. In this case we are showing the signal applied to a 230VAC LED down-light operating from a trailing-edge dimmer. Again, it’s a simple connection and the very high common-mode rejection of the scope means that we can have faith in the accuracy of the displayed signal. Resolution, sampling rate and waveform update rate measure the signals. Isn’t that what you really want from a scope? Scope1 shows one real-world scenario that we came up with for this scope. Channels 1, 2 and 3 are connected across three cells in a fully charged Li-Po battery pack, hence they are each showing around 4.1V (with 2V/div), as confirmed by the measurement at upper left. We’ve staggered the vertical (ground) offsets for each channel so the traces don’t obscure each other. Channel 4 is monitoring the gate voltage of a P-channel Mosfet connected across cell #3. It is held high initially, keeping the Mosfet off. When the Mosfet switches on, it is pulled down to The next most impressive feature of this scope is the combination of 10-bit ADCs and the many different bandwidth options, selectable per-channel: 1/2/5/10/20/50/100/200/500kHz and 1/2/5/10/20/50/100/200/500MHz (the latter options available only on the higher-bandwidth models). Basically, with a very wide bandwidth, there’s enough noise that the 10-bit ADC provides little benefit. But once you reduce it below about 50MHz, the waveform becomes much cleaner and you can really see the advantage of the extra two bits giving 1024 different voltage steps rather than just 256. This, in combination with a 2mV/div sensitivity setting Scope1: channels 1, 2 & 3 (yellow, green & red traces) are connected across three cells in a Li-Po battery while channel 4 (blue trace) shows the floating gate drive of a P-channel Mosfet connected across cell #2. The trigger is set to when the Mosfet switches on. Probe settings are shown at the top and bottom of the screen. Scope2: The yellow and green traces show the complementary drive signals coming from a PIC16F88 microcontroller and these have the same common earth point. The red trace shows the summed drive signal across a piezo transducer which is effectively being driven in bridge mode. siliconchip.com.au June 2016  81 Scope3 and Scope4 show the signal applied to a 230VAC LED dimmable down-light operating from a trailing-edge dimmer. We are using a high voltage 100:1 probe. Note the displayed voltage measurements. Scope3 shows the dimmer at the minimum setting while Scope4 is for a higher power setting. and 1:1 probes allows for much better small signal analysis than with a typical DSO. While some scopes provide a low-pass filter option, they tend to have very limited abilities with it switched on, such as reduced waveform update rate, no MATH operations and so on. With this scope, you can choose a channel bandwidth as low as 1kHz and treat the result just like you would any other trace with no degradation in performance. This allows you to filter out noise and glitches you aren’t interested in to better observe the actual signal. It’s especially useful when working with audio frequency signals. The bandwidth choices in the range are 60MHz, 100MHz, 200MHz, 350MHz and 500MHz. Regardless of which you pay for, you get a 5Gsample/second scope. This is shared between the channels so drops to 2.5Gsa/sec with two active and 1.25Gsa/sec with three or four active. Memory is 500ksamples, shared between the four channels, which is more than adequate but not as large as some desktop scopes. The waveform update rate is up to 50,000 waveforms per second – again, more than adequate and this rivals many desktop scopes but a few high-end units will do more. As with the memory depth, it would be a rare situation where you actually need a higher rate than this. Basically you would only need it if you were searching for very occasional runts or other malformed pulses. Acquisition and triggering Like many modern scopes, in addition to the sample, average and peak-detect acquisition modes, this one offers a high-resolution mode which provides some of the noise-removal properties of averaging mode but can be used with non-repetitive signals. It gives a much cleaner-looking result in many cases so it’s a welcome feature. One thing we’ve noticed in using this scope is that its triggering system seems exceptionally accurate and stable. When using the normal level-based triggering, the trace always seems to cross the intersection of the timebase origin and trigger level perfectly. The basic trigger modes available are Edge, Glitch (positive/negative/both, min/max) and Pulse Width (positive/negative, shorter/longer/inside/outside width). Measurements and other features The RTH1004 can display up to four measurements in the upper-left corner of the screen. If showing more than two, the font shrinks so there’s enough space. Pretty much all the normal measurements are available, eg, 82  Silicon Chip frequency, rise time, fall time, pulse width, duty cycle, average, RMS, peak and overshoot. It can also display power readings such as apparent power and power factor. These measurements require one channel to read the voltage and another the current (via a clamp probe or an external shunt). “MATH” modes are fairly basic and include addition, subtraction, multiplication, absolute value and square. An XY plotting mode is also available. The RTH1004 also has the ability to operate as a data logger and to store and review trace history (with the segmented memory option). Plus it has a number of other features that we won’t go into in detail including mask testing (with beep on failure) and vertical/horizontal cursors. One feature which is missing from the RTH1004 is a spectrum analysis option. However, in our experience, this is not terribly useful on most scopes – you’re generally better off with a separate spectrum analyser if you need this feature. Also, it lacks “probe sensing”, so you have to configure each channel for the correct probe attenuation setting. This is understandable given the isolated BNC sockets used and since the supplied probes are fixed at 10:1 (and likely you will be using these often), it isn’t a huge hassle. Display and user interface The 800 x 480 pixel 7-inch TFT display is bright and offers high contrast and a good viewing angle. It provides 10 horizontal divisions and 8 vertical. There’s an option for a high-contrast colour scheme which makes it easier to view in direct sunlight. The touch-screen interface is far from a gimmick. You don’t have to use it; all functions can be accessed via the push-buttons and wheel and you can even turn off the touch function if you find you’re accidentally activating it. But many functions are much easier (and more intuitive) when accessed via the touchscreen, especially selecting from drop-down lists and navigating through menus. The arrangement of the front panel buttons is a little different than a traditional desktop scope, so it took us a while to figure out which buttons activated some functions. But overall, the RTH1004 is quite easy and simple to use once you have done so. The buttons are large which allows operation even when wearing gloves. Like pretty much all modern scopes, there is a “boot-up” time between switching the unit on and being able to use it but it’s relatively short – just a few seconds. Switch-off is pretty fast and takes about one second. siliconchip.com.au And it does not have a fan, which is a pleasant change from many scopes with quite obtrusive fans. Other options The scope we’re reviewing is a four-channel model and this is the one we would prefer to use in a lab environment where two channels often just aren’t enough. Having said that, the twochannel model (RTH1002) does have one advantage besides a slightly lower price in that it replaces the two missing channels with a multimeter. The four-channel model still has a multimeter mode which works with any combination of the inputs however it will only read voltages and only with a three digit read-out. Also you would probably want to use it with a BNC-to-alligator-clip cable. But if you buy the two-channel model, you get two standard insulated banana sockets to plug standard multimeter probes into and a four-digit readout. While it can’t measure current without an external current clamp or shunt, it does add resistance (up to 100MΩ), diode test, continuity, frequency and capacitance (up to 10,000µF) modes, plus the ability to measure temperature using a platinum RTD. Accuracy is also improved compared to the scope-based DVM with a basic voltage accuracy of 0.05%. While you have to choose between the two and four-channel models initially, everything else can be upgraded later: you can increase the bandwidth, add the logic analyser (eight channels, 250MHz, 125ksample memory), add serial triggering and decoding (I2C, SPI, RS-232/422/485), add advanced triggering modes (TV, runt, interval, etc) and add Wi-Fi or LAN remote control. Size, weight, battery, accessories etc. Battery life is stated as four hours and our use gives us no reason to doubt that. The scope weighs 2.4kg and while it isn’t difficult to carry around, the average person would probably be quite fatigued if they had to carry it for long periods. Luckily it incorporates a fold-out stand and is quite comfortable to use on a bench top or other flat surface. In fact, compared to a standard desktop scope it uses up about half the bench space, being narrower and lacking the front-facing input sockets. Its overall dimensions are 200mm wide, 300mm tall and 74mm deep. The DC barrel charging socket is at lower left, hidden under a flap (to keep moisture and dust out) and it charges in a couple of hours using the supplied mains “brick”. When you plug the charger in, the power button lights up blue and it changes to yellow once the battery is fully charged, so you can tell at a glance. Also hidden under a flap, at the righthand side, is the logic interface socket, USB host and device ports and Ethernet (RJ-45) socket for remote control. The scope is supplied with two or four 10:1 probes depending on the model you buy, as well as the charger/power supply, battery and soft handle which makes it easier to carry one-handed. The probes supplied are high-quality types but they are also quite large and chunky with insulated alligator ground clips on the end of quite long wires. They are good for probing low-frequency, high-voltage siliconchip.com.au equipment but clumsy for hooking into a packed PCB. To be fair, most scopes suffer from the same basic problem – the probes are based on decades-old designs and do not work well with modern electronics which involves much smaller components mounted closer together. And most SMDs have no legs or pins you can easily hook onto. One very nice feature of these probes is that they are supplied with an insulated ground spring clip. This replaces the long ground wire and is necessary for probing high frequency signals (>10MHz say) if you want an accurate idea of the waveform shape. Most probes are supplied with uninsulated springs which are very frustrating to use as unless you are making connections to a set of pads designed to suit the probe, you have to worry about accidentally shorting nearby components to ground. Quirks One oddity we noticed is that when the timebase is set to less than 1ms/div and you freeze the display, it always shows multiple waveforms overlaid, even when persistence is tuned off. If you really need to capture a single waveform at a fast timebase you can use the single trigger mode; however we are in the habit of simply freezing the display using the Run/Stop button in Normal or Auto mode to examine a non-repetitive waveform more closely, so this is baffling behaviour. By the way, there’s no dedicated single trigger button (as is common on many scopes); you need to change the trigger mode to Single and then press the Run/Stop button to capture a waveform. Conclusion and special offer While this scope may not have a full complement of bells and whistles, as a test instrument goes, it’s hard to think of any that are more practical and flexible. And given that you are effectively getting four built-in high-performance isolated differential probes along with a portable, high-bandwidth, high-resolution four-channel DSO, it’s great value. Rohde & Schwarz have two special offers for this product line which are valid until June 30, 2016: Offer #1 (“Lab”): Buy any four-channel R&S Scope Rider model (starting from $5650 ex GST) and get these for free: Mixed signal analysis (RTH-B1), I2C/SPI serial triggering and decoding (RTHK1), UART/RS-232 serial triggering and decoding (RTH-K2) and Advanced triggering (RTH-K19). Offer #2 (“Field”): Buy any two-channel R&S Scope Rider model (starting from $4710 ex GST) and get these for free: Wireless LAN (RTH-K200), Web interface remote control (RTH-K201), Hard shell protective carrying case (RTH-Z4), Car adapter (HA-Z302), Battery charger for Li-Ion Battery (HA-Z303), Replacement battery (HA-Z306), Extended set for RT-ZI10/RT-ZI11 (RT-ZA21). To make an enquiry or purchase, contact a Rohde & Schwarz reseller. For Australia, these are Mektronics (call 1300 788 701 or email sales<at>mektronics. com.au) or Test and Measurement Australia (call (02) 4739 9523 or email sjb<at>TandM. com.au). Or for New Zealand, Nichecom (call (04) 232 3233 or visit www.nichecom.co.nz). Alternatively, you can contact Rohde & Schwarz Australia directly on (02) 8874 5100 or e-mail Sales.Australia<at>rohde-schwarz. SC com June 2016  83