RS Pro RS14 Multimeter

RS Pro RS14 MultimeterImportant: before reading this review, please read this important safety information.

Overview

The RS Pro RS14 is very similar to the BSIDE ADM02 previously reviewed. In fact, I stumbled across the ADM01/02 meters when searching eBay for a visually matching meter - or at least, as best I could from the low-res photo on the RS website - in the months prior to the release of the RS14. They are different, but also share many things in common. At the time - May 2016 - the RS14 cost £17 (including VAT), but since then, I note that it has been discontinued and replaced by a new version in a rather fetching shade of red - and the price has risen to £20.

It's a basic unit that is a re-branded CEM DT-914 - it's also seen with Hayes UK branding. Like the BSIDE ADM02, it's a 2000-count meter with 0.5% basic DC accuracy, and features temperature and microamps. This one is rated to 600V CAT III, but I can't find any evidence of independant verification of this. However, as RS is a massive supplier to the industry, you'd hope and assume that they'd only want to put their name to decent products, and certainly for professional use, it's far better to buy from RS than eBay!

This meter has another advantage over the BSIDE ADM01/02 - a manual range button. This alone might make it worth the extra! The meter uses a 9V PP3 battery, which is included.

Unboxing

The unit comes in a plastic clamshell package rather than a box. As you'd expect from RS, the manual is pretty good. The probes aren't exactly Fluke quality, but are a worthwhile improvement on the BSIDE types. They have removable covers that convert the probes from a claimed CAT IV 600V/CAT III 1000V to CAT II 1000V. A standard thermocouple is included.

RS Pro RS14 - package
      contents

The meter is slightly smaller than the BSIDE types, although most of that difference is caused by the holster (which is also responsible for making the BSIDE meters somewhat thicker than the RS14). The RS14 doesn't have a holster - instead the blue sections are soft-touch over-moulded plastic. In a drop-test, I suspect the BSIDE would perform better because of the holster, but I've yet to try that!

RS Pro RS14 compared
      to the BSIDE ADM02

Operation

Previously I criticised the rotary switch of the B-Side ADM01/02 for being a bit stiff (so therefore hard to change mode with one hand while the unit is stood up on its tilting bail). However, the RS-14 is much worse! On my hardwood bench, it is impossible to change mode without it sliding about the place. On a carpet tile it's better, but you still need to use spare fingers to hold the damn thing still while turning the switch! Really, you need to have it flat on its back. The switch has a rubberised coating to help with grip, and that's very necessary!

But when on its back on a hard surface, it slides about all over the place. The only non-slip elements are at the top behind the display, so offer next to no resistance against the rotation of the mode switch. If only they'd put similar non-slip bumps on the bottom as well. The BSIDE meters are much better here because of the separate holster.

However, the buttons are better than the BSIDE ADM01/02. Rather than hard plastic buttons acting against cheap tact switches, they've used a membrane keypad. Good...

In terms of functionality, the left "MODE" button does the same as it did on the ADM01/02 - changing between AC and DC current, switching between °C and °F, and switching between diode and continuity. The next one is the manual range function that is missing from the ADM01/02 meters. As mentioned, that's good news. You might only need manual ranging occasionally, but when you need it, you need it!

The next button is a combined backlight and Hold button. That's less good - I'll get on to that. Finally, there is the MAX function. Interesting but not especially useful IMHO...

The LCD is much bigger, with larger digits. But the viewing angle is really poor compared to the BSIDE types. If you lay the meter flat on its back - which the stiff switch and hopeless tilting bail more or less obliges you to - then you can hardly read the display because the "off" segments are lit up! It's worse if you're off to the side.

Display of the RS Pro
      RS14 compared to the BSIDE ADM01 and ADM02

They both use the same IC, so some of the annoyances of the BSIDE meters are equally present in the RS14, such as the backlight behaviour; you have to hold the backlight button for 2 seconds to persuade it to come on, and it only stays on for 15 seconds! But with the RS14 it's worse as they've joined the backlight and Hold pins of the IC, with the intention of a brief press engaging the hold function. But the long press needed to get the backlight on also engages Hold, meaning that once you've finally got the damn thing to light up, you have to press the Hold button again to get it out of Hold mode! You'd get use to it, but I was surprised at how annoying that was. Eventually, you just give up trying to use the backlight.

By way of example of how you might do it, the Fluke 87V combines the backlight function with the Hi-res mode. A brief press controls the backlight, and a long press engages Hi-res. As you press the button initially, the backlight comes on (or more precisely, it changes to the next state - on dim, on bright, or off). But if you hold the button long enough to put it into Hi-res mode, the backlight reverts to the mode it was previously in because it's obvious that you didn't want to change the backlight; you wanted to change resolution. Might seem trivial, but as someone who occasionally does a bit of UI design, it's the sort of detail I notice and appreciate when it's obviously been thought about.

The backlight itself is fine, but not as bright as the B-Side models. Interestingly, the ADM02 is considerably brighter than the ADM01, but that's almost certainly because they aren't too strict about the type of LEDs they purchase for these!

In use, the RS14 has the same "overshoot" issue as the BSIDEs. So, set your PSU to 18 volts or thereabouts and dab the probes on the output, and it'll jump to 18.0V rather than 18.00V.

But fortunately, it doesn't suffer from the same AC voltage over-reading as you increase the frequency. Both my BSIDEs do this, so it's not a fault with the first one I bought. The RS14 just falls away as you'd expect - the -3dB point being approximately 7.5kHz (well, on the 2V range - I didn't check the others exhaustively).

Interestingly, the RS14 has an AC mV range that is easy to miss if you don't spot it in the manual. It will never auto-range into that range, but if you press the Range button enough times, you'll get it. Because there is no Range button on the BSIDEs, that mode is not available (and therefore we hve no idea if it actually exists).

Annoyingly, the Diode/Continuity function defaults to Diode, just like the BSIDE meters. It's non-latching again, which is fine if that's all you're used to - but once you've used a Fluke or similar, it's tough to go back. The threshold is 50Ω. Amusingly, the RS manual says both <100Ω and <30Ω! The ADM01 was measured at 10Ω, but the ADM02 is 40Ω (the manual says <100Ω). Clearly, this is not a precisely controlled parameter!

The slow resistance readings noted with the BSIDE is also present here. It's a bit hard to describe, and it's a bit inconsistent. It's not related to the auto-ranging, which is fast. I hooked up a couple of decade boxes to a BSIDE and the RS14, and played around for a good 10 minutes - on average, they're basically as bad as each other, but the RS14 is perhaps slightly quicker.

Current consumption from the PP3 varies between 2.1mA and 2.7mA. When the buzzer sounds in continuity mode, the consumption is 17.2mA, and the backlight takes 4.7mA. When in auto power-down mode, it takes just 5µA. I had a bit of trouble with the low-battery warning, as the indication flickers on and then goes off again as you try to find the threshold - I'm not convinved it's working properly. But it started this at about 6V, which is the expected value for this IC.

Teardown

Removing the battery access door also gives you access to the fuses, although I'm not sure what sort of tool you'd need to remove them! And look carefully through to the PCB, near to the battery wires. Yes, that is a pre-set resistor there - mind the battery lead doesn't trap itself in there and alter the setting!

RS Pro RS14 rear view

Undo the 4 self-tapping screws to remove the rear cover:

RS Pro RS14 - inside view

So it's quite different to the BSIDEs on the inside, which comes as no surprise by this point. We find the same 20mm ceramic fuses as seen in the BSIDE meters, but it looks like they've spent a little bit more on input protection - there's even a MOV in there. The input sockets look quite a bit better too.

The first thing I noticed was the 10A current shunt. There's no preset, unlike the B-Side types, and calibration was performed using a pair of side-cutters. That surprised me!

Next, there's a fair few leaded components. All the divider resistors are axial TH types, mostly stood up on end (and need straightening up!). The obvious improvement over the BSIDE meters is the use of leaded components in the 10M input divider - remember how I pointed out the possibility of a spark jumping the 1.5 or 2 mm between the end-caps of the MELF resistors (R1A and R1B)? Here, that prospect has been eliminated (see R27 and R28 - the 5M, 0.5% types - though I note the B-Side resistors are 0.25%).

To remove the PCB, undo the 4 screws nearest the range switch - don't undo the ones that hold the LCD to the PCB!

RS Pro RS14 - underneath the
      PCB, showing the mode switch

What strikes me at this point is how much more spaced out the tracks are that form the function switch. In most of the other cheap meters I've looked at, they are much closer together, and when subjected to high voltages, arcing between the tracks is a common failure mode. Similarly, the contacts on the switch itself are correspondingly generously spaced. It all helps.

Let's take a closer look at the PCB:

RS Pro RS14 - top view of the PCB

As usual, the OEM model number (DT-914B) is printed on the silk-screen. Trying to follow the input circuitry, it appears that the return for the MOV follows quite a complicated route around the whole of the PCB, creating a large loop. It looks like the PTC and fuseable resistor are included in that loop, so will limit the current that flows, but I also note that a feed of the pre-protection positive input is taken to a section of the function switch, so without reverse-engineering the whole circuit it's not completely obvious how it's supposed to work.

The 9V battery voltage is regulated down to 3V by a regulator that I haven't yet been able to determine from the markings. The decoupling capacitor is made by "Chang". The SO-8 IC is a TL27M2C - a dual low-power op-amp. The IC has a 4MHz crystal.

As with all the cheap meters here, there are no isolation slots routed in the PCB, nor are there shields between the terminals.

As mentioned already, this multimeter uses the same IC (the Fortune Semiconductor FS9952) as the BSIDE ADM01/02.

How about the new version?

We mentioned earlier that this meter has been superseded by a new version in a rather bold red colour scheme. Are there any other changes?

RS Pro RS14 - old and new
      versions

I spent a good while comparing them, but I can't find any differences at all. The LCD viewing angle is much the same, they behave the same functionally, and they are as accurate as each other. Looking inside, the PCB is marked "DT-914B-5A", whereas the blue one is "DT-914B-3A", but having spent an age under a magnifying glass, I didn't discover any material differences between the two. So, that's disappointing!

Conclusions

In a 2-horse race between this and the BSIDE ADM02, it's not an easy call if you're buying this in a hobbyist capacity. As we've already said, for work, you're going to choose this one for the backing of RS, but in many respects, it is better built than the BSIDE ADM02. But it's twice the price.

The RS14 has better leads, better input sockets, a manual ranging button, and it comes with a battery. But it has a much worse display, with very poor viewing angles - that's my biggest complaint about it, and they don't appear to have fixed that with the new model.

The RS14 appears to have been designed with electrical ruggedness in mind, and has a better CAT rating (albeit with no independant verification as far as I can tell).

The RS14 slips around the bench when you try to use it, and has a poor function switch that is far too stiff and really needs 2 hands to operate. The ADM02 isn't brilliant in that regard, but it is better. And I prefer the separate holster of the BSIDE.

When the RS14 was priced at £17, it was closer to call. Now it's crept up to £20, I fall down in favour of the ADM02. However, since first testing these meters, several better options have appeared, so today, I'd buy neither for home use. But I have bought a small batch for use at work.