WP7388 Cheryl, Greg, Fil, Dave: summing unit commissioning.

The summing chassis (D1500265) outputs a temperature set-point control voltage of 4.15V when the control voltage from h1tcscs is 0 Volts. This corresponds to a set-point temperature of 19.6C (this should represent a temperature below the normal operating range, but Greg mentioned it could be too high).

The voltage to setpoint-temperature conversion is 0.21 V/degC (assuming linear with zero crossing).

The voltage being sent by the h1tcscs DAC has two amplitude drops before it is summed with the baseline 4.15V coming from the summing unit. The first is a gain of 0.5 when the differential signal from the General Standards DAC is converted to a single-ended signal. The second is an internal gain of 0.17 in the summing box (see D1500265). Therefore, to increase the temperature set-point by one degree Celsius, from 19.6C to 20.6C, the model should drive the DAC with 8159 counts. This number is obtained by:

8159 counts gives a DAC output of (20./65536.)*8159 = 2.49V

The delta-V voltage at the output of the summing box is then 2.49*0.5*0.17 = +0.21V

When we drove h1tcscs DACs with this number yesterday, the set-point increased by 0.7C instead of 1.0C (read on the LCD panel of the chillers). It looks like we will use empirically derived DAC values if there is a voltage drop on the long haul from the CER to the MR-Mezzanine.