Campbell Scientific CR1000KD CR800 and CR850 Measurement and Control Systems - Page 85

Section 7. Installation Table 4. Current Source and Sink Limits Terminal Limit1 < 1.80 A @ 70°C < 1.50 A @ 85°C 5V + CS I/O (combined)5 < 200 mA 1 "Source" is positive amperage; "sink" is negative amperage (-). 2 Exceeding current limits limits will cause voltage output to become unstable. Voltage should stabilize once current is again reduced to within stated limits. 3 A polyfuse is used to limit power. Result of overload is a voltage drop. To reset, disconnect and allow circuit to cool. Operating at the current limit is OK so long a a little fluctuation can be tolerated. 4 Polyfuse protected. See footnote 3. 5 Current is limited by a current limiting circuit, which holds the current at the maximum by dropping the voltage when the load is too great. 7.4.5.1 Switched Voltage Excitation Two switched, analog-output (excitation) terminals (VX1 - VX2) operate under program control to provide -2500 mVdc to +2500 mVdc excitation. Check the accuracy specification of these channels in CR800 Specifications to understand their limitations. Specifications are only applicable for loads not exceeding ±25 mA. Note Table Current Source and Sink Limits (p. 84) has more information on excitation load capacity. CRBasic instructions that control excitation channels include: • BrFull() • BrFull6W() • BrHalf() • BrHalf3W() • BrHalf4W() • ExciteV() Note Excitation channels can be configured to provide a square-wave ac excitation for use with polarizing bridge sensors through the RevEx parameter of the previously listed bridge instructions. 7.4.5.2 Continuous Regulated (5 Volt) The 5V terminal is regulated and remains near 5 Vdc (±4%) so long as the CR800 supply voltage remains above 9.6 Vdc. It is intended for power sensors or devices requiring a 5-Vdc power supply. It is not intended as an excitation source for bridge measurements. However, measurement of the 5V terminal output, by means of jumpering to an analog input on the same CR800), will facilitate an accurate bridge measurement if 5V must be used. 85