AIC - Instrumentation for Industry and Laboratory

Frequently asked questions

 
Question
I want to use the power supply in the PM4 Panel meter to power my 4-20mA transducer. Can I do that?
Answer
Yes, with a couple of restrictions. Most of the PM4 range of panel meters with 4-20mA inputs offer an regulated 18VDC transmitter supply on both AC and DC powered instruments. The current is limited to 25mA maximum.
 
Many of the PM4 range have an option of an isolated 24VDC (±12VDC) supply. This, too, is limited to 25mA maximum current.
The standard 18VDC supply must not be used if the power supply option is installed.
 
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Question
What is the maximum length for the cable on a pH electrode?
Answer
We recommend a maximum of 10m. Because of the very low level voltage generated by the pH electrode and the high impedance, the cabling is prone to picking up electrical noise. AIC uses special high quality cable with a special "anti-microphonic" layer to minimise this interference. If it is necessary to run longer cables, we suggest the use of a unity gain amplifier. AIC offers such an amplifier - Model Number: PHAMP-A30-BRK-1 or PHAMP-A30-ENC-2 (amplifier in IP65 field mount enclosure).
 
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Question
My pH meter shows a reading of 7 all the time. I've tried recalibration but nothing seems to work!
Answer
A constant reading of 7 is indicative of a short circuit across the electrode or the connections to the instrumentation. In the case of AIC electrodes, one possibility is that the "anti-microphonic" layer in the special electrode cable used by AIC is shorting to the centre conductor. Please refer to our Application Note - Electrode Cable - for details on terminating the cable on a pH or ORP (Redox) electrode.
We recommend that cable be left terminated with the standard BNC connector and an adaptor be used. AIC offers an adaptor under the part number of P-BNC/BP-100.  
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Question
I want to connect up more than one load cell in parallel to my panel mount weight indicator. Are there any problems?
Answer
You must be aware of some restrictions. Firstly, the excitation voltage from the instrumentation needs to be set at 5VDC. Secondly, the impedance of the loadcell combination must not be below 75 Ohms. Most load cells are 350 Ohm impedance but they must be carefully checked and the combination carefully calculated.
 
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Question
I cannot scale the low and high outputs on the analog retransmission of my PM4 Panel Meter!
Answer
Several of the PM4 range offer a Proportional/Integral (PI) control option for the analog retransmission where this option is installed. In the function table there is a function called "rec ctrl". This controls the mode of the analog retransmission operation. If it is set to "on", the analog retransmission is in PI mode and the instrument will not show the functions to set the high and low retransmission values. If "rec ctrl" is set to "off", the functions for high and low are available and the functions for PI control are suppressed.
Put the instrument into "CAL" mode, enter "FUNC" mode then scroll through to "rec ctrl". Make sure it is set to "off". Press the "F" key to accept the change then leave "FUNC" mode. Reenter "FUNC" mode and the high and low setting functions will be available.
 
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Question
What's the difference in load cells?
Answer
Load cells come in many descriptions and types and sometimes it is difficult to decide the type that is best for an application. When should we use a "single point" cell and when should we use a "shearbeam" cell?
Let's define some load cell types with typical examples of use:
Single point load cell
Single point load cells are used by themselves. They are designed to give an accurate reading even if the load is off centre (eccentric). A single point load cell will include its load capacity and a platform size within its specifications. For example, the SG-PT1000 series of single point load cells specify a load platform of up to 350 mm x 350 mm for capacities up to 35 kg and a load platform of 400 mm x 400 mm for capacities up to 250 kg. If a larger platform size is used, the cell will not give an accurate output with eccentric loads outside the platform parameter. Single point load cells are used in platform scale applications for bag filling, check scales, etc.
Shearbeam load cell
Shearbeam load cells are usually used in multiples and in situations where the load is unlikely to be eccentric. Typical examples are under tanks, silos or in weighbrides etc. It is suggested that 3 cells be used under a tank or bin as this gives the best stability. Various mounting options are available. The outputs from the cells can go to a summing box, a multiple input instrument (such as AIC's TP4-WT4) or can be paralleled into a single input monitor. Care must be taken if paralleling load cells to ensure that the excitation power supply is adequate. Paralleling load cells is only recommended when the cells have matched outputs (mV/V figures).
"S-type" load cells
As the name implies, these cells are shaped like an "S". They are universal cells that can undergo compression (they can be squeezed) or tension (they can be stretched). This makes the "S-type" cell very versatile. Mounting options include rod end bearings, load buttons with load cups and spherical feet. These options are designed to minimise off centre loading. A typical application would include measurement of suspended loads from a hoist etc.
Compression load cells
Compression load cells are for compression applications only. That is they are designed to be "squeezed". These cells are excellent in applications under bins, silos etc. The cells are usually "button shaped" and quite compact. It is recommended that 3 or 4 cells be used with 3 cells being preferred for stability. Like shearbeam cells, the outputs can be paralleled if required.
Tension load cells
Tension cells are designed to be stretched only. The typical tension load cell will be bar shaped with attachment holes at each end. A typical application would be to measure the pulling force on a winch or hoist cable.
Rope clamp load cells
Rope clamp load cells are designed to indicate the tension in a lifting cable (or rope) without the necessity of inserting a cell into the rope system (as would need to be done with a tension cell). A rope clamp load cell works by imposing a bend on the cable and then measuring the straightening of the cable as a load is applied. The rope bends the cell and the output is scaled to represent the force or load applied. These cells are used mainly for overload warning applications.
Refer to the Load Cells page for more details and datasheets.
 
 
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