使用说明书手册PHMA

Preamp application GuidePreampCompatibleModelInstrumentsPHMAThe PHMA is a differentialBNCinput pH 2-Wire transmitter.CONNECTORIt can interface with many太display and control devicesrequiring a 4-20mA input.Temp.Comp.NotesPowerGainOutputAuto TC is available in12V to 36V DC,ZERO4-20mA,representing 0-the preamp,using aSingle Supply,and14 pH or down to any 23KQ@25C BALCOCurrent >25mASPANpH portion of that rangeelement.adjust.or ORP spans of±20mVto±2V,Preamp Terminals1-(+)4-20mA Output Signal.Connect the load device to this terminal.Do not connect the power source directly here.2-(-)4-20mA Output Signal.This terminal MUST be connected directly to the negative side of the DC power source.5-3K TC(For ORP ranges,put a fixed resistor of 1Ko to 18KQ between 5 and 6 to achieve desired range.)6-3K TC7-Solution Ground10-BNC Connector (Reference)OPERATING NOTES(1)The unit ships with a 3.01KQ resistor between terminals 5 and 6.If an auto TC is used(3KQ @25C BALCO element only)then the resistor must be removed and the BALCO element connected in its place.(2)When used in the differential input mode,the jumper wire between terminals 7 and 10 must be removed and a lead run from 7to a metal contact in the stream within 12 inches of the pH electrode.This metal piece is called a"solution ground".When it isused,the pH glass and reference cell potentials are individually compared to the potentiai of the solution ground eiectrode andthese two values are then subtracted to give the pH potential.The advantage of this approach is that the reference cell isconnected to the high impedance input of an amplifier,isolating it from ground loop currents.Ground loops occur when earthground is connected to some part of the signal loop.If the reference cell is connected to DC common when this happens,acurrent will flow from the unwanted earth connection,through the reference,to the earth ground contacts in the sample stream.Because the reference cell has electrical resistance,the ground loop current will produce an error voltage across it that is addeddirectly to the pH signal.(3)Wire the unit exactly as shown on the label.It is particulariy important to connect the negative side of the DC power sourcedirectly to preamp terminal 2.(4)Internal protective resistors will prevent circuit damage from temporary reversed polarity of the power connections.Leavingthe preamp in this condition for longer than 5 minutes will cause the resistor to overheat and probably open.(5)The amplifier has a stiff filter stage which eliminates practically all noise spikes,but it also slows response so that the fulleffect of a step change in pH value will not be seen for 45 seconds.To reduce or eliminate this feature.remove the bottom coverof the amp and remove one or both of the capacitors from their sockets.Substituting smaller values for the caps will reduce theamount of filtration.