Eppley started making standard voltage cells in 1917 through the 1990s. In the 1960s they started making instrumentation for the measurement of solar irradiance and atmospheric irradiance and are still in that business.
The Weston Cell (see patents below) (Wiki) was the first electrochemical (Wiki) voltage reference cell and was the standard definition of the Volt from 1911 to 1990.
The Eppley patents allowed for a cell that could be shipped rather than one that needed to be hand carried so that it always pointed up. The chemical composition of the Eppley cell was more stable than the Weston Cell.
Using the HP 34401 in 6 digit mode and default 10 Meg Ohm input impedance it reads: 1.018367 Volts.
At 10 Gig Ohm input resistance it reads: 1.018447. It's 76 F inside and 91 F outside.
A short time later it's: 1.018451.
Eppley EPP 811381 Standard Cell in Box
Raw Eppley EPP 811381 Standard Cell
E.M.F. 1.0192 (the 1.019 was printed on the card & 2 was hand written.
I got interested in these after doing some research on the Campbell-Stokes Sunshine Recorder. As it happens I already had the Eppley standard cell so put them both on this web page.
"A pyranometer (Wiki) is a type of actinometer used to measure broadband solar irradiance on a planar surface and is a sensor that is designed to measure the solar radiation flux density (in watts per metre square) from a field of view of 180 degrees."
When narrow bands are measured the device may be called a Radiometer, like the Exotech 100AX.
Precision Pyranometer, Model PSP
This unit covers 285 to 2800 nanometers.
The output is 7.4 mv in direct afternoon sun (28 Apr 2014 39N, 123 W) and current of 2 micro amps.
This is normal. Email from factory:
"Model 2 or PSP Pyranometer #12250F3 was supplied without a calibration performed which is why there is nothing on the label.
If you assume 7 mV / cal / cm2 / min (or in SI Units = 10 uV / Wm-2) then you have
7.4/7 = 1.06 Langley per minute (1 Langley = 1 Cal / cm2) or in SI Units 7.4/10*1000 = 740 Wm-2 (watts per meter squared)."
A Pyrheliometer (Wiki) is similar device except in this case is more like a telescope that's aimed at the sun.
Fig 2 PT02H-4P (?) connector on unit
Mating connector is MS3116P8-4S
Fig 3 Desiccant (Wiki) Window
Fig 4 Top view
Note the bubble level can be adjusted relative
to the base plate by using 3 hex screws to attract
and 3 hex screws to repel.
Fig 5 Label
Type _?_ Model 2 s/n: 12205F-3
This radiometer has been compared
with the Eppley group of reference
standards. The derived value of the
constant for this instrument is:
____?___ millivolts/cal-cm^-2 Min&-1 (Int.)
A Thermopile (Wiki) converts thermal energy into electrical energy.
128 Ohms. Slit wedges removed: Direct Sun: 3 mV or 3 uA?
Have reinstalled the slit blocks and aligned them so only the center most 12 devices are illuminated.
Now 4.3 mV or about 3 uA. Maybe the other row of thermopiles are the cold junction?
How precise should the alignment of the slit be?
Fig 2 "4" and "3" stamped into slit groove.
The slit blocks are stamped "3" and "4".
That allows matching the block to the slot
for a very tight fit.
Inside of back cover is black.
Fig 3 24 junctions hand made.
This was advertised on eBay as an Eppley item, but that's not the case, it's made by Thermo Electric. It does however contain a standard cell.
It's intended for testing potentiometers (like the Leeds Northroup), measuring temperature of a type-K thermocouple (Wiki) in deg C or voltage in mV.
The reason it was for sale is probably that the internal "D" battery had leaked and there was corrosion on the battery holder.
I have made a pdf version of the manual including bookmarks and color photos for the MiniMite and MultiMite, ask if you want to buy a copy.
Cleaned battery holder contacts.
Turned switch from Transit Lock to Operate and used (-) screwdriver to zero meter.
Held switch in Operate and turned Std Adj to zero meter.
So it should be ready to measure either mV or a type-K thermocouple as selected by the Range switch.
With a paperclip shorting the + and - inputs, in Operate Mode, when the scale wheel at the bottom is adjusted so the meter reads zero the mV scale reads zero (it does not matter which range you use).
Fig 3 The standard cell is in the diagonal holder.
A Radiometer (Wiki) is any device that measures radiant flux (Wiki: Radiometry) or electromagnetic radiation (Wiki). Many devices do this for example: Light meters that work using photo-voltaic principles, Radiation Detectors that use Geiger-Muller tubes or other radiation sensitive devices, Ultraviolet sensors, IR sensors, Pyranometers, thermopiles, . . .
The Crooke Radiometer (Wiki: Light Mill) was invented in 1876 by William Crookes (Wiki).
182172 Apparatus for Indicating Intensity of Radiation, W. Crookes, Sept 12, 1876, 356/216; 244/1R; 60/641.13; 244/172.7; 244/168 -
This device can be used as a photometer (sheet 2, Fig 4) (Wiki, Weston 594)to compare the light output of say a gas lamp with a standard candle by reflecting a narrow beam of light from a mirror and watching where it hits a scale.
This is a very practical device, not a toy.
The bulb was mounted to the base at an angle. So when sitting on a level surface the the edge of the open glass tube rubs against the support needle. The friction keeps the paddles from turning.
YSI (Wiki) Kettering (Wiki) Radiometer Model 65A
Charles F. Kettering (Wiki) was involved the automotive ignitions, starting systems, Etc.
Back many decades I used YSI thermistors because HP sold them. The specifications were very tight. See my sensors web page for Thermistors.
Range: 0.2 to 40 microns wavelength flatness to +/- 1%. Uses a balanced pair of thermistors (Reference and Detector).
This is the only radiometer I know of that uses a thermistor as the sensor. It makes sense that YSI would do this because they are probably the pinnacle thermistor maker.
Thermopiles are made by Eppley, Newport, Coherent, Moleotron, Melles Griot, Raytek, Gentec, LaserBee, Betatherm, Kip & Zonen, Scientech . . .
I'm guessing you zero the meter with the port closed after letting the whole system come to thermal equilibrium. Then the port cover is hinged open and a reading made.
Fig 3 No. 3 Rubber stopper to allow sensor to be in chamber (with gas?).
Fig 4 Sensor easy to replace. It's what the patent 3387134 is about, see below.
Fig 5 Orange, Violet and Red wires to XLR jack (Wiki).
The AD235J is a precision
Dual Thermocouple sensor wiring.
1639412 Indicator for heat rays, Mechau Robert, Carl Zeiss, 1927-08-16, 136/214; 338/15; 374/130; 338/11; 338/25- uses ether hot wire bolometer or thermopile
2761072 Total-radiation pyrometer, Eric M Wormser, Servo Corp of America, 1956-08-28, 250/233; 246/DIG.1; 250/347; 356/43; 359/366; 374/129; 374/130 -
3387134 Wavelength independent, direct reading radiometer, Richard W Treharne, Charles Kettering Foundation, Yellow Springs, Ohio, (YSI) 1968-06-04, 250/349; 374/133; 338/18 - this is the Model 65 sensor.
Sensing thermistor (24, Wiki) and reference thermistor (18) are measured in a Wheatstone Bridge (Wiki).
Other radiometers use thermopiles. Maybe the thermistor is not as flat in response at different wavelengths?
The patent shows a switch for Calibrate or Operate, but this unit does not have that switch.
3392624 Flashing-light spectrophotometer with monochromatic monitoring, Ke Bacon, Richard W Treharne, Charlton K Mckibben, Charles Kettering Foundation, Yellow Springs, Ohio, (YSI),1968-07-16, 356/317; 356/419; 356/416 - a pair of strobe lights, photo-multiplier & tubes.
3444739 Radiant energy measuring instrument, Richard W Treharne, Charles Kettering Foundation, Yellow Springs, Ohio, (YSI), 1969-05-20, 374/128; 250/353; 374/168; 250/338.1; 374/133- hand held, transistors, uses reference and sensor thermistors. Citations (9), Cited by (26)
3586439 Direct reading pyrometer employing pyroelectric crystal detector, Charlton K Mckibben, Richard W Treharne, Kettering Scientific Research Inc, 1971-06-22, 356/43; 136/213; 250/338.3; 250/353; 359/230; 374/130; 374/126 - A lead zirconium titanate crystal possessing pyroelectric characteristics is employed in a direct reading pyrometer for measuring directly the temperature of an object (first use of Pb[ZrxTi1−x]O3)
3600611 Elasto-optic device with mechanical bias, Richard W Treharne, Charles Kettering Foundation, Yellow Springs, Ohio, (YSI), 1971-08-17, 359/286; 310/328; 310/311 - a modulator. for use on optical bench
Latimer Clark (Wiki) 1873 Clark Cell -
" at 15 °C was defined by the International Electrical Congress as 1.434 volts, and this definition became law in the United States in 1894 (Weston Cell)."
310004 Galvanic Battery, Edward Weston, Dec 31, 1884, 429/125 -
439737 Standard Galvanic Cell, Edward Weston, Nov 4, 1890, 429/125 - requires temperature controlled water bath.
Wiki: Galvanic Cell
485089 Standard cell for electric batteries, H. S. Carhart, Oct 25, 1892, 429/125; 429/222 -
Mentions prior art by Latimer Clark of England 1873 defects:
1. Would not endure transportation because of the mixing up of the contents of the cell, causing short-circuiting and initiating chemi cal action fatal to the use of the cell,
2. subject to more or less local action, which limited the life of the cell,
3. its change of electro-motive force with tem perature, technically called its “temperature coefficient, is large and apparently variable.
494827 Voltaic cell, Edward Weston, Apr 4, 1893, 429/125; 204/408; 429/222 - standard "H" type voltage cell, maybe the first "H" type cell? - very temperature stable,
also see the Weston Model One meter.
From the Eppley web page: "The Eppley Laboratory was founded in Newport, RI by Captain Marion Eppley in 1917 for the purpose of supplying Weston Standard Cells at the request of the Leeds & Northrup Company"
Wiki: Weston Cell - "...it was adopted as the International Standard for EMF from 1911 until superseded by the Josephson voltage standard in 1990."
631044 Standard voltaic cell, Richard O Heinrich, Weston Electric Inst Corp, Aug 15, 1899, 429/101; 429/125 - improvement on 494827 "H" type standard cell.
Note photos of the ID plate on some early Weston standard cells show a patent date of Aug 16, 1899 z(Wednesday) which is in error, the correct date is Aug 15, 1899 which is a Tuesday. As far as I know all patents have been published on a Tuesday.
1081365 Thermopile, William W Coblentz (licensed to Eppley), Oct 28, 1913, 136/213 - the basis of the Eppley Laboratory Thermopiles and probably the PSP
Oldest patent with 136/213 as primary classification.
2613234 Plug or septum for electrolytic cells, Eppley Marion, Eppley Lab Inc, Nov 19, 1949, 429/125, 429/185
2816946 Cadmium st andard cell,George D Vincent, Eppley Lab Inc, Jul 20, 1956, 429/125, 429/185
Campbell Stokes Sunshine Recorder
Dent Meridian Instrument - Dipleidscope
Digital Photography 204: Studio Flash - triggers SkyScan like lightening
Heathkit ID-4001 Weather Station
Oregon Scientific BAR122HGLA indoor WWVB clock, barometer, temperature, humidity & THGN321ES outdoor temperature and humidity.
IR Cloud Sensor
Seismometer & Geophone
Sensors - extensive page with many sensor types
SkyScan Severe Thunderstorm Detector
Soil Moisture Instruments
SD_Pat2 Sundial Patents
TMQ-34 Meteorological Measuring Set -
Weston Model One meter -
TM 750-5-3 lists the GVH-1 Solar Radation Measuring Set.
Standard Cells, Their Construction, Maintenance, and Characteristics by Walter J. Hamer, National Bureau of Standards Monograph 84, January 15, 1965.
PRC68, Alphanumeric index to web pages, Products for Sale, Contact
Page created 25 April 2014