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Hach dr/2000 spectrophotometer: completely rebuilt
Here is a completely rebuilt Hach model DR/2000 microprocessor-controlled, single beam spectrophotometer in top condition (Photos #1 and #2).
The little brother of, and a portable alternative to, the famous Hach DR/3000, the DR/2000 is primarily designed for water-quality analysis, and for operator convenience, this instrument is pre-programmed for more than 120 standard tests (see Photo #3 of the stored program list, version 3.2). But the DR/2000 can be manually programmed for up to 50 tests not already stored in memory, so its actual applications are virtually unlimited.
* Stored Programs. These include more than 120 industry-standard test procedures pre-programmed into the instrument by Hach.
* Manual Program for tests not already stored in the instrument s memory. In this mode, the operator can program in his own custom test procedures, and complete instructions are provided in the operator s manual.
* The DR/2000 is a visible wavelength instrument with a working range of 400nm to 900nm.
For indoor use, the Hach DR/2000 runs on standard 115 volt household current via an external 8 volt d.c. power supply (aka a battery eliminator , shown in Photos #1 & #2).
For outdoor use and fieldwork, the DR/2000 uses an 8 volt, sealed, rechargeable battery, and for charging this battery, the d.c. power supply described above doubles as the battery charger.
The Hach DR/2000 is a wonderful instrument, but like all pieces of lab equipment, it contains components that, with normal usage, will eventually wear out and fail, so before I sell as DR/2000, I replace all of these parts with new ones, even if they seem to be working fine. The following is a list of the new parts installed in this instrument.
The new parts installed in this instrument are:
* A new wavelength potentiometer (Photo #4). The monochromator is the optical heart of the instrument, and to convert the exact position of its optics into an electronic signal that the instrument s computer can read, the DR/2000 uses a high-precision potentiometer. When these electro-mechanical devices become dirty or worn out, it becomes impossible to make wavelength adjustments. In a significant percentage of the DR/2000s I receive, these potentiometers are malfunctioning, so I now install new potentiometers in all the instruments I sell. This instrument has a brand new wavelength potentiometer.
* A new lithium battery (Photo #5). When this lithium battery fails, the instrument s RAM (random access memory) is lost when the instrument loses power. This does not effect the Hach-supplied programs stored in the instrument s permanent eprom chip (also shown in Photo #5), but anything stored in RAM (like user-entered programs) is lost.
This battery is the soldered-in type. Because it s difficult to replace, and the main circuit board must be removed in the process, my rebuild procedure includes the installation of a new lithium battery. Once installed, the lifetime of the new battery is approximately 8 years. This great extension of the instrument s trouble-free RAM operation makes it well worth the investment.
* A new RS232 jack, a new power supply jack, and a new recorder jack (Photo #6). When a DR/2000 is exposed to moisture or a corrosive environment, these components will tarnish and rust, and when that happens, they become unusable. Though they re comparatively minor items, it s a nuisance to have to replace them, so my rebuild process includes the installation of new jacks. This instrument has a new RS232 jack, a new power supply jack, and a new recorder jack.
* A new rechargeable battery (Photo #7). In virtually all the instruments I receive, this battery is either missing or dead, so I install a new one. This instrument has a brand new, 3.2 amp-hour rechargeable battery. When the instrument is plugged into the a.c. power converter (as when it s used indoors), the power converter charges the battery and maintains the charge. When the instrument is unplugged, the battery automatically takes over, and provides 2 to 3 hours of constant-on field operation; even more in the intermittent mode.
* A new set of rubber cabinet feet. Because the rubber feet on the instruments I receive are invariably dried and cracked, I ve installed a set of 4 new rubber cabinet feet.
* And finally, a brand new lamp (Photo #14).
When I receive a DR/2000, I completely disassemble the instrument. Then I clean everything, including the monochromator s optics (very important), the sample chamber, the electronic circuit boards, and the instrument s case.
In most of the instruments I receive, the mechanical wavelength-adjustment mechanism is stiffened or sometimes jammed with dried grease, so I completely disassemble it, ultrasonically clean its parts, and reassemble it with the proper lubricants. Photo #8 shows the reassembled monochromator with the cleaned and lubed wavelength mechanism and the new wavelength potentiometer, ready for reinstallation. You can see the old potentiometer lying in the foreground.
In some of the DR/2000s I receive, I find that one or more of the sample chamber s optical components (originally mounted with silicone) has come loose, resulting in an erratic detector signal and correspondingly unstable readings. To eliminate even the possibility that this might happen again, I completely remove these components. Then I clean them and re-cement them with epoxy. I replace the components listed above, and then I reassemble the instrument.
When the cleaning, repairs, component replacement, and reassembly are finished, I do a 3-point calibration at 442 nm, 633 nm, and 812.5 nm, and I use the same narrow-band interference filters that Hach uses. Photo #9 shows these 3 filters, and just beneath them, the results of my post-calibration tests.
Hach specifies a calibration accuracy of + or 2 nanometers at 422nm and 633 nm, and + or 3 nanometers at 812.5 nm. As you can see, the instrument peaks just 1 nm high with the 442 nm filter, and the peaks are right on the money with the 633 nm and 812.5 nm filters.
Next, with 3 neutral density filters, I test the instrument s photometric accuracy at 440 nm, 590 nm, and 650 nm. These filters are part of a complete test-filter set, calibrated against a set of master filters calibrated at the National Institute of Standards and Technology in Maryland.
Composite photo #10 shows the filter set at the top, the relevant expected readings (highlighted in yellow), and the instrument s actual photometric readings at the bottom. As you can see, the readings are all well within the guaranteed accuracy of the filters.
And finally, I demonstrate the instrument using certified Hach DR/Check standards for a simulated absorbency run, and their DPD-Chlorine-LR standards for 3 simulated colorimetric tests.
Composite Photo #11 shows the DR/Check test kit at the top, and a close-up of the certificate of analysis in the middle. This instrument s actual absorbency readings are at the bottom, and their locations correspond to the locations of the expected readings on the certificate. The numbers on the certificate provide a range of typical readings that you might expect to see with these standards. As indicated on the certificate, I took absorbency readings at wavelengths of 420, 520, 560, and 610 nanometers, and you can clearly see that this instrument is working fine at all the required wavelengths.
Composite Photo #12 shows the DPD-Chlorine-LR test kit at the top, and the relevant part of the certificate of analysis (the part that applies to the DR/2000) in the middle. The actual colorimetric readings are at the bottom, and their locations correspond to the locations of the expected readings on the certificate. The numbers on the certificate provide a range of typical readings that you might expect to see with these standards. I took the readings with the DR/2000 s stored program #85 for average free-and-total chlorine, and, as with the absorbency readings, you can see that the instrument s colorimetric functions are working fine.
Photo #13 shows a very important accessory that you don t normally get with a DR/2000. It s a test standard adapter that locates Hach s certified test standards at exactly the proper height and position needed for an accurate reading, and it s also used with Hach s Accuvac ampoules. The left side of the photo shows the adapter sitting next to a certified chlorine standard (not included), and the right side shows how the standard fits in the adapter. The standard goes in the adapter, and the adapter fits in the instrument; it s that simple.
With larger instruments like the Hach DR/3000, I provide two new lamps free of charge. But the lamps are inexpensive, and lamp alignment is done by the owner on-site.
With the DR/2000, to reduce its size and maximize its portability, the design engineers eliminated the mechanism that allowed for on-site alignment, and they replaced it with a pre-aligned and miniaturized lamp assembly .
These assemblies are more expensive to make so they cost more. The one for the DR/2000 is Hach part #4664700 with a current price of $62. At that price I can t afford to give two of them away, so with the DR/2000s I provide one new lamp. This instrument has a brand new lamp. Note also that these lamps have an average operating life of about 1,500 hours.
Important note about the packaging. I do not charge for packaging these instruments. The packaging is free.
Photo #1. A picture of the instrument with the sample compartment open.
Photo #2. A picture of the instrument with the sample compartment closed.
Photo #4. The new wavelength potentiometer.
Photo #5. The new lithium battery.
Photo #6. The new RS232 jack, the new power supply jack, and the new recorder jack.
Photo #7. The new rechargeable battey.
Photo #8. The cleaned, lubed, and reassembled monochromator with its new potentiometer. You can see the old potentiometer lying in the foreground.
Photo #9. My 3 calibration filters, and the results of the post-calibration tests. Note that you can t see any color in the filter on the right because, at 812.5 nm, its transmission window is in the near-infrared at the upper limit of human vision.
Photo #10. My test-filter set and the results of the photometric tests.
Photo #11. These absorbency test results using certified Hach standards show that this instrument s absorbency functions are all working properly.
Photo #12. These colorimetric test results using certified Hach standards show that this instrument s colorimetric functions are all working properly..
Photo #13. A picture of the custom-machined test standard/Accuvac adapter that I'll provide free with this instrument.
Photo #13. A picture of the new lamp. Note that these lamps have an average operating life of about 1,500 hours.
