最近因為安哥的 海水討論文
https://www.ph84.idv.tw/forum/threads/384923/
可能有很多人開始爬鹽度的文章吧~
回顧一下這篇, 發現我好像沒有把 MA887 鹽度計介紹一下, 所以就來補充一下~
ps: 若是會在海圈玩很久, 這台機器值得投資~
英文大部分都是擷取 MA887 說明書的內容:
The MA887 refractometer is an optical device that is simple and quick to use.
Samples are measured after a simple user calibration with distilled or deionized water.
Within seconds, the refractive index and temperature are measured and converted into one of three popular measurement units:
Practical Salinity Units (PSU)
Salinity in parts per thousand (ppt)
Specific Gravity (S.G. (20/20))
All conversion algorithms are based upon respected scientific publications using the physical properties of seawater (not sodium chloride).
以上內容簡單來說如下敘述:
1. MA887 是台光學折射計, 在簡單的校正程序後,
測試 折射率 與 溫度, 用 演算法計算出 鹽度.
ps: 校正程序使用 RO水歸零, 可能是要校正不同溫度下, 折射率的改變量,
因此讓整台機器溫度恆定後再 校正 與 測試 非常重要!
2. 有三個不同單位表示鹽度:
PSU
PPt
S.G.(20/20)
[PSU]
PSU is defined as the conductivity ratio of seawater to a standard KCl solution. It is based upon the work
of the UNESCO, ICES, SCOR and IAPSO. This information is published in The Joint Panel of Oceanographic Tables and Standards.
Practical Salinity Scale 1978 (PSS-78)
A standard seawater of 35 has by definition a conductivity ratio of unity at 15°C with a KCl solution containing a mass of 32.4356 g KCl in a mass of 1 kg of solution.
定義:
在溫度15°C, 海水導電度 = KCl 導電度 (KCl濃度 32.4356g/1kg) 時, PSU=35
ps: PSU是沒有單位的.
[PPt]
An older salinity scale is ppt (10-3), where salinity is defined by “the salt content is the weight of the inorganic salts contained in 1kg of seawater if all bromide and iodide are replaced by an equivalent amount of oxides”
(Knudsen, 1901)
定義:
PPt = 鹽的重量 / 1kg 海水重量
ex: 3.5g NaCl + 96.5g 水 ,總重量100g
sea-water contains 96% NaCl
鹽度(PPt) = (3.5 / 100)x 96% = 33.6
依據
TEOS-10 (Thermodynamic Equation Of Seawater - 2010), 兩者關係:
Sa(ppt) = Sp(psu)*1.004715
=> 機器測出來的 PPt 數值都會比 PSU 來的大. (應該就只是數值換算, 並非實際測量導電度)
[SG(20/20)]
Specific Gravity (20/20) ia based upon the published relationship between density at 20 °C and the mass of dissolved salts in the seawater sample
(CRC Handbook of Chemistry and Physics, 87th)Edition).
定義:
在溫度20°C
Specific Gravity (20/20) = 待測物密度 / 參考物(標準海水)密度
有很多其他的光學比重計, 參考物並不一定是 20 °C 標準海水!
會改變比重值因素太多了, 建議還是用鹽度ppt 當作目標值比較好用~
