Figure 6-3. Example of OBS -1P array; AM, BM, or PO 

 Instrument characteristics 



The OBS series of sensors are mature instrumentation. Their characteris- 

 tics include a linear response to suspended particulates (see below), a wide 

 dynamic range, and a 10-Hz bandwidth. The OBS-1P have built in tempera- 

 ture compensation to reduce sensor drift. The NSTS sensors have a voltage 

 output range of + 5 V, and the OBS-1P output range is to 3.5 V. Conse- 

 quently, for the same sensor gain (and sensitivity), the NSTS sensors have a 

 greater dynamic range than the OBS-1P. 



The 12-bit analog to digital converter (A/D) used to record all OBS sensors 

 was the PC-Mate Lab Master by Tecmar Inc. (now Scientific Solutions), and 

 it sampled all sensors simultaneously (sample and hold) at a 10-Hz rate. Be- 

 cause all of the OBS have different (though comparable) responses to suspend- 

 ed particulates, their absolute sensitivity is limited by the 12-bit resolution of 

 the A/D. For one-bit accuracy and a typical sensor response of 10 g/£/V, the 

 resolution of the A/D is 0.04 gIL 



Chapter 6 Suspended Sediment Concentration 



111 



