Couple of points here, if you are asking about digital density meters is it because you just want a digital display or are you looking for the fiscal measurement accuracy that goes with that term?
Note also that while various density meters may appear to have the same performance according to the specifications published, these usually refer to the performance at 20degC and you then need to explore what happens away from the lab calibration conditions. As Shakespear says, "not all that glisters is gold".
Points to look for are temperature effects; velocity of sound effects, pressure effects (and beware pulsating pressure with bent tube devices, cross talk, and then calibration... how many fluids?
The term "Coriolis" density meter needs explanation, this refers to coriolis meters that also measure density. Density is a function of the resonant frequencyu of operation not the coriolis effect. In vibrating tube density meters there is also a coriolis effect present. Solartron exploited this when they were the first to introduce single straight tube density meters (full bore) but the design is based on one optimised for density and it never had the coriolis performance of dedicated coriolis meters. The micromotion Elite claims to have density measurement performance of a fiscal standard. Not all other "coriolis" density meters have this performance.
Krohnes single straight tube mass meter has a lot of inovative features that would have helped Solartron, had they continued their own mass flow meter, but it has no bellows and has a more significant temperature effect on density.
Groovy mentions Viscosity. I did a check on the Krohne site and did not find this referenced. Viscosity measurement is a valuable quality parameter and indicator of other quality parameters. Again we come up against the old conundrum of whether to go for multi-functionality in a single instrument. Buying a mass meter for viscosity measurement is a lot to pay if you don't need the other parameters. What viscosity performance do you get and how valuable is the measurement? Micromotion used to offer viscosity measurement based around their "D" type mass flow. There is no mystery to this method, it simply used pressure drop emasurement across the tube and the familiar relationship between pressure drop, flow and viscosity. IF this is what Krohne offer, then why? This approach cannot offer the performance of a dedicated process viscometer. Today there are many digital viscometers available for the process environemant. Again, not all are as good as each other but they can equal the performance of a process capillary viscometer which the dP across a mass meter cannot.
SO far as i know there is only one mass meter that measures viscosity without using the pressure drop approach but i believe this uses amplitude measurement not bandwidth so is not digital. I don't know how it performs.
Mass flow meters do have the potential to measure density, mass flow rate and viscosity all at once. However, if that method depends on the amplitude, i doubt the performance and because of the construction of such devices i also doubt the performance if they were able to manage the trick of making a bandwidth measurement (for viscosity)at the same time they make a phase shift measurement (for flow).
However, if anmyone has any information to the contrary or can reference any data on coriolis meter viscosity performance i would be very greatful.
Bottom line, what accuracy do you need? and do you really need that density span? Both are key points in choosing your instrument.
