Pearl 8000 data logger from Electronic Innovations Ltd. is a product which may interest anyone who uses their Beeb as a laboratory instrument. It is a neatly-made device which could help schools, engineers or anyone else who wants to use the analogue port to measure changing values. Its design does much to overcome the limited accuracy of the BBC's ADC analogue port.

For the readers unfamiliar with this subject, a data logger is a device which can be used to monitor one or more signals. It samples each one at defined rates for a defined time and stores the results for later analysis.

Strictly, the Pearl (Parallel Entry Auto Ranging Logger) 8000 is not a data logger. However, when plugged into the Beeb, the whole system does become one, so the distinction is subtle.

The Pearl 8000 is built into a metal box, which measures approximately 10" x 7" x 2.5", and finished in BBC cream. It is connected to the computer's analogue and user ports by 2 ribbon cables. The front panel has 8 spring-loaded connectors, one for each channel which can be monitored, and a 9th connector as an earth. There are also 8 LEDs to show which channel is being read at any time. A 25-pin D socket at the back of the box provides a way of extending the channels and the device's control signals to a distant point. The standard of construction is good and shows careful attention to detail in its component and track layout.

The Pearl 8000 is controlled via the user port, by software supplied with the device, and it multiplexes up to 8 separate channels to ADC channel 1. A useful feature is that it is not limited by the usual 0-1.8V input range of the ADC. A key feature of the device is that it incorporates a software controlled attenuator which will reduce signals of up to 250V to suitable levels for the ADC.

The system can therefore be used to measure voltages (DC only) with absolute values from 0 to 250V. Since it also detects a reversed polarity, its full range is actually -250V to +250V. Although high voltages are reduced to measurable levels, small values are not amplified, so that although it will read down to a millivolt or so, the precision and accuracy of the low readings is poor (a precision amplifier is planned for the future).

The Pearl 8000 also overcomes the limited accuracy of the Beeb's standard ADC. The 7002 chip used in the computer relies on having a reference voltage supplied to it against which it measures all incoming voltages. The standard system has a nominal 1.8V reference, but it is fairly crude and therefore inaccurate. The Pearl 8000, however, provides a dedicated reference, using a precision 1.225V diode.

This approach greatly increases the system's accuracy, although it does nothing for the ADC's basic 10 bit (at best) precision. If you're not sure of the difference between accuracy and precision, suppose you measure a 0.5V signal and get a reading of 1.3675234V. You have measured with great precision, but the accuracy is lousy. The point is that the Pearl 8000, for all its vast cost, in fact contains no analogue to digital converter. It uses the Beeb's own, and just supplies it with a stable reference source.

A specialist device like the Pearl 8000 is almost certainly going to be used by people who understand what it can do for them and what they want to do with it. The instructions reflect this approach but, even so, the draft manual I reviewed left much to be desired. The manufacturers tell me that the manual will be improved but that they assume that users will know what they are doing. I fear that this might be a little optimistic!

For example, there was a serious lack of general-purpose software. The supplied programs were tricky to follow and would not be easy to adapt for purposes other than demonstration. Some of the programming techniques were individualistic to say the least, and all the software was optimised for the demos. It is unlikely, for instance, that any "real" programs would want to poke the readings from the 8 ports directly into the 8 integer variables A%-H%. There were not even sufficient guidelines on what should be considered when writing new software for the device.

That said, how did the system behave? Using the demonstration programs, very well. It was simple to use and acted as advertised. The system was accurate and, especially when taking several readings from each channel to reduce the effects of noise, the differences between the channels were insignificant. For example, applying a precision 10.0V to each channel, and averaging 10 readings from each, gave values between 9.991V and 10.002V. Not surprisingly, the variation was a little wider when taking only one sample from each channel: 9.988V to 10.022V. Still pretty good, though.

While the system is thus impressively accurate, I did notice that the supplied software incorporated individual calibration figures for the Pearl 8000. Given the system's design, individual calibration would be hard to avoid, but could concern anybody using more than one. The suppliers claim, however, that individual units should not differ by more than 0.5%.

Who might use the Pearl 8000? Virtually anyone who might want to use a BBC to monitor and record DC voltages. The voltages themselves could represent almost any physical item - pressure, temperature, speed, pH, the list is almost endless. It allows up to 8 voltages (11 if you want to fiddle a bit) to be measured, compared with the 4 available from the standard ADC port and, very importantly, the accuracy is much improved

Probably, the system would be of most use in schools or colleges, but I can imagine some hobbyists putting it to good use too. It could even be of value in small laboratories or in simple test equipment. Couple it with my recent chart recorder program (Beebug Vol. 5 No. 10) and you would have an even more useful tool.

The Pearl 8000 is a nicely-made and effective piece of hardware which adds significantly to the Beeb's capabilities. It gives you 8 input channels when the Beeb only provides 4, and it increases the accuracy of measurement considerably, as well as providing a voltage attenuator. But for what it does, it is certainly a little pricey.

Like too many add-ons, it is let down by its software and documentation. It would not be difficult for Electronic Innovations to improve them but, unless the company does so, it will remain unnecessarily difficult to exploit the system properly.

Note: The manual and software available to our reviewer are early versions. Production versions will in both cases be much improved according to the manufacturer.