MEASUREMENT TECHNIQUES:
Dranetz 658
www.dranetz-bmi.com

Note: This is a self generated review. Dranetz BMI have never made contact with me.

A fairly well-known instrument to many. Sold as "a digitising oscilloscope, a true RMS volt and ammeter, a harmonic distortion analyser, a power disturbance monitor, and a strip chart recorder". Apart from the last, slightly over-stated feature, this pretty much sums it up.

Everything is configurable via the front panel. Although to the user this may be seen as an advantage, it is also a huge temptation for a client who wants to see if there is anything that may be of use to the power quality investigator (and also has an opportunity to erase what he does not want anyone to see!).

A somewhat cumbersome device and is generally thought of as a devil to set up (yet coming from an electronics background where oscilloscopes were the order of the day, I need to be honest and say I found this a very easy instrument to drive).

Its 'bulkiness' does hide the fact this is an all-in-one instrument comprising the capturing hardware, display, data entry panel, and printer - and not forgetting the disk drive that allows for data to be transferred to a PC without the need for cables and proximity. This is a decided plus for this instrument.

This allows the instrument to be some distance from the person viewing the data, as long as there is a means to get the diskette to the viewer. Another problem is one cannot just "read" the data without some rather pricey software (and I personally don't think the software's value-for-money factor is that great).

The input impedance is 40MW, the maximum voltage input is rated at 600Vrms, but the instrument can read to 724Vrms (1024V peak or DC). Added to this, there are no multipliers so using dividers to extend the input range will result in mental arithmetic on a regular basis.

The current inputs are 120W, and not a standard voltage for full scale (e.g. 1V or 2V). Even the current into the input is not some understandable figure such as 10mA or 20mA full scale. The unit I have appears to be set at about 1.45V full scale. However, I do have a simple two resistor change to bring the unit to a high impedance 1V input.

It's a little too keen to trigger an event and has a tendency to 'overstate' the problem (many have found themselves chasing red herrings because of this!), but nothing a bit of lateral thinking (coupled with years of experience) doesn't sort out afterwards.

What I don't think is user friendly is the very noisy fan, and that some bright spark thought it wise that the input sockets must be at the back! It is not happy when asked to work much outside room temperature (reports of not starting up if too hot/cold are common place). Although it has some logging features, it does miss some very fundamental requirements to call it a genuine power quality logger or recorder.

Dranetz-BMI have newer models but no-one from the company has bothered to contact me so, sadly, I cannot prove or dispute the unfavourable reports I have heard about them - both the instruments and the company.

On the instrument side, having now seen the 4300, I am not surprised! This is a very disjointed instrument to set up and I can see many users needing a number of attempts to get the desired recording.

And on later platforms, one needs a dongle for the software meaning you have no means to view your prized data after handing back a hired or loaned instrument. I view this latest move as nothing short of Dranetz-BMI holding potential customers to ramsom! I will personally never buy any new gear from them because of this.

I would not be surprised if this move spells the start of the end as it has already caused the software to lose favour, and if the software loses favour so will the instruments... and finally the company. And talking of the company, when I tried to get some technical support on the 658 all I got was a mouthful from a salesman!

In such a competative market, this is one company not showing itself any good!

However, let me not end on a bad note; As for the 658, this is an excellent 4-channel 'instantaneous view' PQ-DSO. If you have one, hold on to it. Combined with a full disclosure recorder, as featured in the next category, will have you coping with pretty much everything regarding power quality measurements.

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©  03.05.03 / 15.07.04